View source for Polio

{{short description|Infectious disease caused by poliovirus}}
{{redirect|Poliomyelitis|the virus|Poliovirus|other uses|Polio (disambiguation)}}
{{pp-semi-indef}}
{{Use dmy dates|date=March 2022}}
{{Infobox medical condition (new)
| name          = Polio
| synonyms      = Poliomyelitis, infantile paralysis, Heine–Medin disease
| image         = Polio lores134.jpg
| caption       = A man with a [[Wasting|wasted]] right leg due to poliomyelitis
| field         = [[Neurology]], [[Infectious disease (medical specialty)|infectious disease]]
| pronounce     = {{IPAc-en|ˌ|p|oʊ|l|i|oʊ|ˌ|m|aɪ|ə|'|l|aɪ|t|ᵻ|s}}
| symptoms      = Fever, sore throat<ref name=PinkBook2021/>
| complications = [[Muscle weakness]] resulting in [[flaccid paralysis|paralysis]];<ref name=PinkBook2021/> [[Post-polio syndrome]]<ref name=NIH2014Post/>
| onset         =
| duration      =
| causes        = [[Poliovirus]] spread by [[fecal–oral route]]<ref name=PinkBook2021/>
| risks         = Poor hygiene
| diagnosis     = Finding the virus in the [[feces]] or [[antibodies]] in the blood<ref name=PinkBook2021/>
| differential  =
| prevention    = [[Polio vaccine]]<ref name=WHO2014/>
| treatment     = No treatment other than [[supportive care]]<ref name=WHO2014/>
| medication    =
| prognosis     =
| frequency     = 30 (wild) + 856 (vaccine-derived) in 2022<ref name="WHO2018Epi">{{cite web |title=This page allows you to request a table with AFP/polio data |url=https://extranet.who.int/polis/public/CaseCount.aspx |url-status=live |website=WHO |access-date=3 May 2023 |archive-url=https://web.archive.org/web/20150402165939/https://extranet.who.int/polis/public/CaseCount.aspx |archive-date=2 April 2015}}</ref>
| deaths        =
| alt           = Polio survivor
| types         = Wild PV types 1,2 & 3; vaccine-derived PV<ref name=PinkBook2021/>
}}
<!--Definition and symptoms-->

'''Poliomyelitis''' ({{IPAc-en|ˌ|p|oʊ|l|i|oʊ|ˌ|m|aɪ|ə|ˈ|l|aɪ|t|ɪ|s}} {{respell|POH|lee|oh|MY|ə|LY|tiss}}), commonly shortened to '''polio''', is an [[infectious disease]] caused by the [[poliovirus]].<ref name="PinkBook2021" /> Approximately 75% of cases are [[asymptomatic]];<ref name="ECDC">{{cite web |title=Disease factsheet about poliomyelitis |url=https://www.ecdc.europa.eu/en/poliomyelitis/facts |website=European Centre for Disease Prevention and Control |date=26 March 2013 |access-date=12 April 2023 |archive-date=12 April 2023 |archive-url=https://web.archive.org/web/20230412204733/https://www.ecdc.europa.eu/en/poliomyelitis/facts |url-status=live}}</ref> mild symptoms which can occur include sore throat and fever; in a proportion of cases more severe symptoms develop such as [[headache]], neck stiffness, and [[paresthesia]].<ref name="PinkBook2021" /><ref name="WHO2014" /> These symptoms usually pass within one or two weeks. A less common symptom is permanent [[Flaccid paralysis|paralysis]], and possible death in extreme cases.<ref name="PinkBook2021">{{cite book |last1=Estivariz |first1=Concepcion F. |last2=Link-Gelles |first2=Ruth |author2-link=Ruth Link-Gelles |last3=Shimabukuro |first3=Tom | editor-last1= Hall |editor-first1=Elisha |editor-last2=Wodi |editor-first2=A. Patricia |editor-last3=Hamborsky |editor-first3= Jennifer |editor-last4=Morelli |editor-first4=Valerie |editor-last5=Schillie |editor-first5=Sarah |edition=14th|year=2021 |chapter=Chapter 18: Poliomyelitis |chapter-url=https://www.cdc.gov/pinkbook/hcp/table-of-contents/chapter-18-poliomyelitis.html |title=Epidemiology and Prevention of Vaccine-Preventable Diseases (The Pink Book) |url=https://www.cdc.gov/pinkbook/hcp/table-of-contents/|url-status=live |publisher=[[Centers for Disease Control and Prevention]] (CDC, US) |archive-url=https://web.archive.org/web/20220317195113/https://www.cdc.gov/vaccines/pubs/pinkbook/polio.html | archive-date=17 March 2022}}.</ref> Years after recovery, [[post-polio syndrome]] may occur, with a slow development of muscle weakness similar to what the person had during the initial infection.<ref name="NIH2014Post">{{cite web |title=Post-Polio Syndrome Fact Sheet |url=http://www.ninds.nih.gov/disorders/post_polio/detail_post_polio.htm |publisher=NIH |access-date=4 November 2014 |date=16 April 2014 |archive-url=https://web.archive.org/web/20110729090555/http://www.ninds.nih.gov/disorders/post_polio/detail_post_polio.htm |archive-date=29 July 2011}}</ref>

<!--Cause and diagnosis-->
Polio occurs naturally only in humans.<ref name="PinkBook2021" /> It is highly infectious, and is spread from person to person either through [[fecal–oral route|fecal–oral transmission]]<ref name="PinkBook2021" /><ref>{{cite web |last=CDC |date=2022-03-29 |title=What is Polio? |url=https://www.cdc.gov/polio/what-is-polio/index.htm |access-date=2022-04-24 |website=Centers for Disease Control and Prevention |archive-date=14 November 2020 |archive-url=https://web.archive.org/web/20201114175849/https://www.cdc.gov/polio/what-is-polio/index.htm |url-status=live}}</ref> (e.g. poor hygiene, or by ingestion of food or water contaminated by human feces), or via the oral–oral route. Those who are infected may spread the disease for up to six weeks even if no symptoms are present. The disease may be diagnosed by finding the virus in the [[feces]] or detecting [[antibodies]] against it in the blood.<ref name="PinkBook2021" />

<!--Epidemiology-->
Poliomyelitis has existed for thousands of years, with depictions of the disease in ancient art.<ref name="PinkBook2021" /> The disease was first recognized as a distinct condition by the English [[physician]] [[Michael Underwood (physician)|Michael Underwood]] in 1789,<ref name="PinkBook2021" /><ref>{{cite book |last1=Underwood |first1=Michael |author1-link=Michael Underwood (physician) |url=https://archive.org/details/b28771254_0002/page/52/mode/2up |title=A Treatise on the Diseases of Children |date=1789 |publisher=J. Mathews |volume=2 |location=London, England |pages=53–57}}</ref> and the virus that causes it was first identified in 1909 by the Austrian [[immunologist]] [[Karl Landsteiner]].<ref>{{cite book |url=https://books.google.com/books?id=BTQKnkpN6qQC&pg=PA11 |title=Polio |date=1999 |publisher=University of Rochester Press |isbn=978-1-58046-066-8 |veditors=Daniel TM, Robbins FC |edition=1st |location=Rochester, NY |page=11 |archive-url=https://web.archive.org/web/20160617223604/https://books.google.com/books?id=BTQKnkpN6qQC&pg=PA11 |archive-date=17 June 2016 |url-status=live}}</ref><ref>{{cite journal |last1=Landsteiner |first1=Karl |author1-link=Karl Landsteiner |last2=Popper |first2=Erwin |author2-link=Erwin Popper |date=1909 |title=Übertragung der Poliomyelitis acuta auf Affen |trans-title=Transmission of Poliomyelitis acuta to monkeys |url=https://babel.hathitrust.org/cgi/pt?id=uc1.b3208372&view=1up&seq=389&skin=2021 |journal=Zeitschrift für Immunitätsforschung und experimentelle Therapie [Journal for Research on Immunity and Experimental Therapy] |language=de |volume=2 |issue=4 |pages=377–390 |access-date=9 September 2021 |archive-date=9 September 2021 |archive-url=https://web.archive.org/web/20210909224922/https://babel.hathitrust.org/cgi/pt?id=uc1.b3208372&view=1up&seq=389&skin=2021 |url-status=live}}</ref> Major [[epidemic|outbreaks]] started to occur in the late 19th century in Europe and the [[United States]],<ref name="PinkBook2021" /> and in the 20th century, it became one of the most worrying [[List of childhood diseases|childhood diseases]].<ref>{{cite book |url=https://books.google.com/books?id=3p7jezlQ0zgC&pg=PA11 |title=Science and practice of pediatric critical care medicine |date=2009 |publisher=Springer |isbn=978-1-84800-921-9 |veditors=Wheeler DS, Wong HR, Shanley TP |location=London |pages=10–11 |archive-url=https://web.archive.org/web/20160617234650/https://books.google.com/books?id=3p7jezlQ0zgC&pg=PA11 |archive-date=17 June 2016 |url-status=live}}</ref> Following the introduction of polio vaccines in the 1950s, polio incidence declined rapidly.<ref name="PinkBook2021" /> {{As of|2023|October}}, only Pakistan and Afghanistan remain endemic for wild poliovirus (WPV).<ref>{{cite web |title=Poliomyelitis |url=https://www.who.int/news-room/fact-sheets/detail/poliomyelitis |access-date=2024-08-09 |website=www.who.int}}</ref> 

<!--Treatment-->
Once infected, there is no specific treatment.<ref name="WHO2014" /> The disease can be prevented by the [[polio vaccine]], with multiple doses required for lifelong protection.<ref name="WHO2014" /> There are two broad types of polio vaccine; an injected polio vaccine (IPV) using [[Inactivated vaccine|inactivated]] poliovirus and an oral polio vaccine (OPV)  containing [[Attenuated vaccine|attenuated]] (weakened) live virus.<ref name="PinkBook2021" />  Through the use of both types of vaccine, incidence of wild polio has decreased from an estimated 350,000 cases in 1988<ref name="WHO2014">{{cite web|title=Poliomyelitis: Key facts|url=https://www.who.int/en/news-room/fact-sheets/detail/poliomyelitis|publisher=World Health Organisation|date=22 July 2019|url-status=live|archive-url=https://web.archive.org/web/20170418105535/http://www.who.int/mediacentre/factsheets/fs114/en/|archive-date=18 April 2017}}</ref> to 30 confirmed cases in 2022, confined to just three countries.<ref name="GPEI2022-05">{{cite web |last=World Health Organization |date=Jan 3, 2023 |title=Global Wild Poliovirus 2016 - 2022 |url=https://polioeradication.org/wp-content/uploads/2023/01/weekly-polio-analyses-WPV-20230103.pdf |url-status=deviated |archive-url=https://web.archive.org/web/20230108200614/https://polioeradication.org/wp-content/uploads/2023/01/weekly-polio-analyses-WPV-20230103.pdf |archive-date=2023-01-08 |access-date=3 May 2023 |website=Global Polio Eradication Initiative – World Health Organization}}</ref>  In rare cases, the traditional OPV was able to revert to a virulent form. An improved oral vaccine with greater genetic stability (nOPV2) was developed and granted full licensure and prequalification by the World Health Organization in December 2023.<ref name="www.cdc.gov2022">{{cite web |date=2022-05-06 |title=Polio Vaccine: Vaccine-Derived Poliovirus {{!}} CDC |url=https://www.cdc.gov/vaccines/vpd/polio/hcp/vaccine-derived-poliovirus-faq.html |access-date=2022-06-27 |website=www.cdc.gov |archive-date=27 October 2021 |archive-url=https://web.archive.org/web/20211027123224/https://www.cdc.gov/vaccines/vpd/polio/hcp/vaccine-derived-poliovirus-faq.html/ |url-status=live}}</ref><ref>{{Cite web |date=19 February 2024 |title=GPEI-What's next for the novel oral polio vaccine type 2 (nOPV2) now that it's been WHO-prequalified? |url=https://polioeradication.org/news/whats-next-for-the-novel-oral-polio-vaccine-type-2-nopv2-now-that-its-been-who-prequalified/ |access-date=2025-03-26 |website=Global Polio Eradication Initiative |language=en-GB}}</ref>
[[File:En.Video-Polio.webm|thumb|upright=1.2|Video summary of polio ([[Wikipedia:VideoWiki/Polio|Script]])]]
{{TOC limit|3}}

== Signs and symptoms ==
{| class = "wikitable" style = "float:right; font-size:90%; margin-left:15px"
|+'''Outcomes of poliovirus infection in children'''
|-
! style="background:#efefef;" | Outcome
! style="background:#efefef" | Proportion of cases<ref name = PinkBook2021/>
|-
| No symptoms
| style="text-align:center;"|72%
|-
| Minor illness
| style="text-align:center;"|24%
|-
|Nonparalytic aseptic<br /> meningitis
| style="text-align:center;"|1–5%
|-
|Paralytic poliomyelitis
| style="text-align:center;"|0.1–0.5%
|-
|— Spinal polio
| style="text-align:center;"|79% of paralytic cases
|-
|— Bulbospinal polio
| style="text-align:center;"|19% of paralytic cases
|-
|— Bulbar polio
| style="text-align:center;"|2% of paralytic cases
|}

The term "poliomyelitis" is used to identify the disease caused by any of the three [[Serovar|serotypes]] of poliovirus. Two basic patterns of polio infection are described: a minor illness that does not involve the [[central nervous system]] (CNS), sometimes called abortive poliomyelitis, and a major illness involving the CNS, which may be paralytic or nonparalytic.<ref>{{cite journal |vauthors=Falconer M, Bollenbach E |title=Late functional loss in nonparalytic polio |journal=American Journal of Physical Medicine & Rehabilitation |volume=79 |issue=1 |pages=19–23 |year=2000 |pmid=10678598 |doi=10.1097/00002060-200001000-00006}}</ref> Adults are more likely to develop symptoms, including severe symptoms, than children.<ref name="PinkBook2021" />

In most people with a [[Immunocompetent|normal immune system]], a poliovirus infection is [[Subclinical infection|asymptomatic]]. In about 25% of cases, the infection produces minor symptoms which may include [[Pharyngitis|sore throat]] and low fever.<ref name="WHO2014" /><ref name="ECDC" /> These symptoms are temporary and full recovery occurs within one or two weeks.<ref name="PinkBook2021" /><ref name="WHO2014" />

In about 1 percent of infections the virus can migrate from the gastrointestinal tract into the central nervous system (CNS).<ref name="PinkBook2021" /> Most patients with CNS involvement develop nonparalytic [[aseptic meningitis]], with symptoms of headache, neck, back, abdominal and extremity pain, fever, vomiting, stomach pain, [[lethargy]], and irritability.<ref name="Chamberlin_2005">{{cite book |url=https://archive.org/details/isbn_9780787691516 |title=The Gale Encyclopedia of Neurological Disorders |publisher=Thomson Gale |year=2005 |isbn=978-0-7876-9150-9 |veditors=Chamberlin SL, Narins B |location=Detroit |pages=1859–70 |url-access=registration}}</ref><ref>{{cite web |last=CDC |date=2022-03-29 |title=What is Polio? |url=https://www.cdc.gov/polio/what-is-polio/index.htm |access-date=2022-04-24 |website=Centers for Disease Control and Prevention |archive-date=14 November 2020 |archive-url=https://web.archive.org/web/20201114175849/https://www.cdc.gov/polio/what-is-polio/index.htm |url-status=live}}</ref><ref name="Late">{{cite book |vauthors=Leboeuf C |title=The late effects of Polio: Information For Health Care Providers. |url=http://www.health.qld.gov.au/polio/gp/GP_Manual.pdf | publisher=Commonwealth Department of Community Services and Health |year = 1992 |isbn=978-1-875412-05-1 |access-date=23 August 2008 |archive-url = https://web.archive.org/web/20080625212726/http://www.health.qld.gov.au/polio/gp/GP_Manual.pdf |archive-date = 25 June 2008}}</ref> About one to five in 1,000 cases progress to [[paralytic]] disease, in which the muscles become weak, floppy and poorly controlled, and, finally, completely paralyzed; this condition is known as [[Flaccid paralysis|acute flaccid paralysis]].<ref name="Henry1" /> The weakness most often involves the legs, but may less commonly involve the muscles of the head, neck, and [[Thoracic diaphragm|diaphragm]].<ref name="PinkBook2021" /> Depending on the site of paralysis, paralytic poliomyelitis is classified as spinal, [[medulla oblongata|bulbar]], or bulbospinal. In those who develop paralysis, between 2 and 10 percent die as the paralysis affects the breathing muscles.<ref name="WHO2014" />

[[Encephalitis]], an infection of the brain tissue itself, can occur in rare cases, and is usually restricted to infants. It is characterized by confusion, changes in mental status, headaches, fever, and, less commonly, [[seizure]]s and [[spastic paralysis]].<ref name="Encephalitis">{{cite book | vauthors = Wood LD, Hall JB, Schmidt GD |title=Principles of Critical Care |url=https://archive.org/details/principlescritic00hall_433 |url-access=limited |edition=3rd |publisher=McGraw-Hill Professional |year=2005 |page=[https://archive.org/details/principlescritic00hall_433/page/n897 870] |isbn=978-0-07-141640-5 }}</ref>

== Etymology ==
The term ''poliomyelitis'' derives from the [[Ancient Greek]] {{transliteration|grc|poliós}} ({{lang|grc|πολιός}}), meaning "grey", {{transliteration|grc|myelós}} ({{lang|grc|µυελός}} "marrow"), referring to the grey matter of the [[spinal cord]], and the suffix ''[[wikt:-itis|-itis]]'', which denotes [[inflammation]],<ref name="Chamberlin_2005" /> i.e., inflammation of the spinal cord's grey matter. The word was first used in 1874 and is attributed to the German physician [[Adolf Kussmaul]].<ref>{{cite web |title=Definition of POLIOMYELITIS |url=https://www.merriam-webster.com/dictionary/poliomyelitis |access-date=2024-04-09 |website=www.merriam-webster.com}}</ref> The first recorded use of the abbreviated version  ''polio'' was in the ''[[The Indianapolis Star|Indianapolis Star]]'' in 1911.<ref>{{cite web |date=9 April 2024 |title=Polio, n. meanings, etymology |url=https://www.oed.com/dictionary/polio_n?tl=true |access-date=9 April 2024 |website=Oxford English Dictionary}}</ref>

== Cause ==
{{main|Poliovirus}}
[[File:Polio EM PHIL 1875 lores.PNG|thumb|right|A [[Transmission electron microscopy|transmission electron microscope]] [[micrograph]] of poliovirus]]
Poliomyelitis does not affect any species other than humans.<ref name="Sherris">{{cite book |url=https://archive.org/details/sherrismedicalmi00ryan |title=Sherris Medical Microbiology |publisher=McGraw Hill |year=2004 |isbn=978-0-8385-8529-0 |veditors=Ryan KJ, Ray CG |edition=4th |pages=[https://archive.org/details/sherrismedicalmi00ryan/page/n552 535]–37 |chapter=Enteroviruses |url-access=limited}}</ref> The disease is caused by infection with a member of the [[genus]] ''[[Enterovirus]]'' known as [[poliovirus]] (PV). This group of [[RNA virus]]es colonize the [[Human gastrointestinal tract|gastrointestinal tract]]<ref name=Harrison>{{cite book| author = Cohen JI| chapter = Chapter 175: Enteroviruses and Reoviruses| title = Harrison's Principles of Internal Medicine| veditors = [[Dennis Kasper|Kasper DL]], [[Eugene Braunwald|Braunwald E]], [[Anthony Fauci|Fauci AS]], etal | edition = 16th | publisher = McGraw-Hill Professional| year = 2004| page = 1144| isbn = 978-0-07-140235-4 | title-link = Harrison's Principles of Internal Medicine}}</ref>&nbsp;– specifically the [[oropharynx]] and the [[intestine]]. Its [[Virus structure|structure]] is quite simple, composed of a single [[sense (molecular biology)|(+) sense]] [[RNA]] [[genome]] enclosed in a protein shell called a [[capsid]].<ref name=Sherris /> In addition to protecting the virus' genetic material, the capsid proteins enable poliovirus to infect certain types of cells. Three [[serovar|serotypes]] of poliovirus have been identified&nbsp;– wild poliovirus type 1 (WPV1), type 2 (WPV2), and type 3 (WPV3)&nbsp;– each with a slightly different capsid protein.<ref>{{cite book | vauthors = Katz SL, Gershon AA, [[Saul Krugman|Krugman S]], Hotez PJ |title=Krugman's infectious diseases of children |url=https://archive.org/details/krugmansinfectio00gers_995 |url-access=limited |publisher=Mosby |location=St. Louis |year=2004 |pages=[https://archive.org/details/krugmansinfectio00gers_995/page/n220 81]–97 |isbn=978-0-323-01756-5 }}</ref> All three are extremely [[virulence|virulent]] and produce the same disease symptoms.<ref name=Sherris /> WPV1 is the most commonly encountered form, and the one most closely associated with paralysis.<ref name="Ohri">{{cite journal |vauthors=Ohri LK, Marquess JG |year=1999 |title=Polio: Will We Soon Vanquish an Old Enemy? |url=http://www.medscape.com/viewarticle/416890 |journal=Drug Benefit Trends |volume=11 |issue=6 |pages=41–54 |archive-url=https://web.archive.org/web/20040204232019/http://www.medscape.com/viewarticle/416890 |archive-date=4 February 2004 |access-date=23 August 2008}} (Available free on [[Medscape]]; registration required.)</ref> WPV2 was certified as eradicated in 2015 and WPV3 certified as eradicated in 2019.<ref>{{Cite web |title=Two out of three wild poliovirus strains eradicated |url=https://www.who.int/news-room/feature-stories/detail/two-out-of-three-wild-poliovirus-strains-eradicated |access-date=2022-08-28 |website=www.who.int |archive-date=30 October 2019 |archive-url=https://web.archive.org/web/20191030210736/https://www.who.int/news-room/feature-stories/detail/two-out-of-three-wild-poliovirus-strains-eradicated |url-status=live }}</ref>

The [[incubation period]] (from exposure to the first signs and symptoms) ranges from three to six days for nonparalytic polio. If the disease progresses to cause paralysis, this occurs within 7 to 21 days.<ref name="PinkBook2021" />

Individuals who are exposed to the virus, either through infection or by [[immunization]] via [[polio vaccine]], develop [[immunity (medical)|immunity]]. In immune individuals, [[IgA]] [[antibodies]] against poliovirus are present in the [[tonsil]]s and [[gastrointestinal tract]] and able to block [[Viral replication|virus replication]]; [[Immunoglobulin G|IgG]] and [[Immunoglobulin M|IgM]] antibodies against PV can prevent the spread of the virus to motor neurons of the [[central nervous system]].<ref name="Kew_2005">{{cite journal |vauthors=Kew OM, Sutter RW, de Gourville EM, Dowdle WR, Pallansch MA |year=2005 |title=Vaccine-derived polioviruses and the endgame strategy for global polio eradication |url=https://zenodo.org/record/1235033 |journal=Annual Review of Microbiology |volume=59 |issue=1 |pages=587–635 |doi=10.1146/annurev.micro.58.030603.123625 |pmid=16153180 |access-date=30 June 2019 |archive-date=9 July 2020 |archive-url=https://web.archive.org/web/20200709053801/https://zenodo.org/record/1235033 |url-status=live }}</ref> Infection or vaccination with one serotype of poliovirus does not provide immunity against the other serotypes, and full immunity requires exposure to each serotype.<ref name=Kew_2005/>

A rare condition with a similar presentation, nonpoliovirus poliomyelitis, may result from infections with [[enterovirus]]es other than poliovirus.<ref>{{cite journal | vauthors = Gorson KC, Ropper AH | title = Nonpoliovirus poliomyelitis simulating Guillain-Barré syndrome | journal = Archives of Neurology | volume = 58 | issue = 9 | pages = 1460–64 | date = September 2001 | pmid = 11559319 | doi = 10.1001/archneur.58.9.1460 | doi-access =  }}</ref>

The oral polio vaccine, which has been in use since 1961,<ref name="WHO2016">{{cite journal |vauthors=((World Health Organization)) |date=2016 |title=Polio vaccines: WHO position paper – March, 2016 |journal=Weekly Epidemiological Record |volume=91 |issue=12 |pages=145–68 |pmid=27039410 |hdl-access=free |hdl=10665/254399}}</ref> contains [[Attenuated vaccine|weakened]] viruses that can replicate. On rare occasions, these may be transmitted from the vaccinated person to other people; in communities with [[Herd immunity|good vaccine coverage]], transmission is limited, and the virus dies out. In communities with low vaccine coverage, this weakened virus may continue to circulate and, over time may mutate and revert to a virulent form.<ref>{{Cite web |title=What is vaccine-derived polio? |url=https://www.gavi.org/vaccineswork/what-vaccine-derived-polio |access-date=2022-08-28 |website=www.gavi.org |archive-date=28 August 2022 |archive-url=https://web.archive.org/web/20220828160534/https://www.gavi.org/vaccineswork/what-vaccine-derived-polio |url-status=live }}</ref> Polio arising from this cause is referred to as ''circulating vaccine-derived poliovirus'' (cVDPV) or ''variant poliovirus'' in order to distinguish it from the natural or "wild" poliovirus (WPV).<ref>{{Cite web |title=GPEI-Vaccine-Derived Polioviruses |url=https://polioeradication.org/polio-today/polio-prevention/the-virus/vaccine-derived-polio-viruses/ |access-date=2022-08-28 |archive-date=28 August 2022 |archive-url=https://web.archive.org/web/20220828160534/https://polioeradication.org/polio-today/polio-prevention/the-virus/vaccine-derived-polio-viruses/ |url-status=live }}</ref>

=== Transmission ===
Poliomyelitis is highly contagious. The disease is [[Transmission (medicine)|transmitted]] primarily via the [[fecal–oral route]], by ingesting contaminated food or water. It is occasionally transmitted via the oral–oral route.<ref name="PinkBook2021" /> It is seasonal in [[temperate climate]]s, with peak transmission occurring in summer and autumn. These seasonal differences are far less pronounced in [[tropical climate|tropical]] areas.<ref name="Kew_2005" /> Polio is most infectious between 7 and 10 days before and after the appearance of symptoms, but transmission is possible as long as the virus remains in the saliva or feces. Virus particles can be  excreted in the [[feces]] for up to six weeks.<ref name="ECDC" />

Factors that increase the risk of polio infection include [[pregnancy]],<ref name="Evans_1960">{{cite journal |vauthors=Evans CA |date=December 1960 |title=Factors influencing the occurrence of illness during naturally acquired poliomyelitis virus infections |journal=Bacteriological Reviews |volume=24 |issue=4 |pages=341–52 |doi=10.1128/MMBR.24.4.341-352.1960 |pmc=441061 |pmid=13697553}}</ref> being very old or very young, [[immune deficiency]],<ref>{{Citation |title=Polio and the late effects of polio |url=https://www.betterhealth.vic.gov.au/health/conditionsandtreatments/polio-and-post-polio-syndrome |access-date=2023-04-12 |publisher=Department of Health, State Government of Victoria, Australia |archive-date=12 April 2023 |archive-url=https://web.archive.org/web/20230412211550/https://www.betterhealth.vic.gov.au/health/conditionsandtreatments/polio-and-post-polio-syndrome |url-status=live }}</ref> and [[malnutrition]].<ref>{{cite journal | vauthors = Chandra RK | title = Reduced secretory antibody response to live attenuated measles and poliovirus vaccines in malnourished children | journal = British Medical Journal | volume = 2 | issue = 5971 | pages = 583–5 | date = June 1975 | pmid = 1131622 | pmc = 1673535 | doi = 10.1136/bmj.2.5971.583 }}</ref> Although the virus can cross the [[placenta|maternal-fetal barrier]] during pregnancy, the fetus does not appear to be affected by either maternal infection or polio vaccination.<ref name=UK>{{cite book |veditors=((Joint Committee on Vaccination and Immunisation)), Salisbury A, Ramsay M, Noakes K |title=Chapter 26:Poliomyelitis. ''in:'' Immunisation Against Infectious Disease, 2006 |url=http://www.immunisation.nhs.uk/files/GB_26_polio.pdf |publisher=[[Office of Public Sector Information|Stationery Office]] |location=Edinburgh |year=2006 |pages=313–29 |isbn=978-0-11-322528-6 |archive-url=https://web.archive.org/web/20090326085852/http://www.immunisation.nhs.uk/files/GB_26_polio.pdf |archive-date=26 March 2009 |access-date=9 March 2007 }}</ref> Maternal antibodies also cross the [[placenta]], providing [[passive immunity]] that protects the infant from polio infection during the first few months of life.<ref>{{cite journal | vauthors = Sauerbrei A, Groh A, Bischoff A, Prager J, Wutzler P | title = Antibodies against vaccine-preventable diseases in pregnant women and their offspring in the eastern part of Germany | journal = Medical Microbiology and Immunology | volume = 190 | issue = 4 | pages = 167–72 | date = March 2002 | pmid = 12005329 | doi = 10.1007/s00430-001-0100-3 | s2cid = 12369344 | doi-access = free }}</ref>

== Pathophysiology ==
[[File:Polio spine.png|thumb|left|A photomicrograph of the lumbar spinal cord depicting an [[infarct]] due to Polio Type III surrounding the anterior spinal artery]]

Poliovirus enters the body through the mouth, infecting the first cells with which it comes in contact&nbsp;– the [[human pharynx|pharynx]] and [[intestinal mucosa]]. It gains entry by binding to an [[Immunoglobulin|immunoglobulin-like]] receptor, known as the poliovirus receptor or [[CD155]], on the cell membrane.<ref name=He>{{cite journal | vauthors = He Y, Mueller S, Chipman PR, et al | title = Complexes of poliovirus serotypes with their common cellular receptor, CD155 | journal = Journal of Virology | volume = 77 | issue = 8 | pages = 4827–35 | date = April 2003 | pmid = 12663789 | pmc = 152153 | doi = 10.1128/JVI.77.8.4827-4835.2003 }}</ref> The virus then hijacks the [[Host (biology)|host cell's]] own machinery, and begins to [[viral replication|replicate]]. Poliovirus divides within gastrointestinal cells for about a week, from where it spreads to the [[tonsils]] (specifically the [[follicular dendritic cell]]s residing within the tonsilar [[germinal center]]s), the intestinal [[lymphoid tissue]] including the [[Microfold cell|M cells]] of [[Peyer's patches]], and the deep [[Cervical lymph nodes|cervical]] and [[Inferior mesenteric lymph nodes|mesenteric lymph nodes]], where it multiplies abundantly. The virus is subsequently absorbed into the bloodstream.<ref name=Baron>{{cite book| vauthors = Yin-Murphy M, Almond JW| chapter = Picornaviruses: The Enteroviruses: Polioviruses| title = Baron's Medical Microbiology| veditors = Baron S, etal | edition = 4th| publisher = Univ of Texas Medical Branch| year = 1996| pmid = 21413259| chapter-url = https://www.ncbi.nlm.nih.gov/books/NBK7687/| isbn = 978-0-9631172-1-2| url-status = live| archive-url = https://web.archive.org/web/20081207154734/http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=mmed.section.2862| archive-date = 7 December 2008}}</ref>

Known as [[viremia]], the presence of a virus in the bloodstream enables it to be widely distributed throughout the body. Poliovirus can survive and multiply within the blood and lymphatics for long periods of time, sometimes as long as 17 weeks.<ref>{{cite web | author = Todar K | title = Polio | work = Ken Todar's Microbial World | publisher = University of Wisconsin – Madison | year = 2006 | url = http://textbookofbacteriology.net/themicrobialworld/Polio.html | access-date = 23 April 2007 | archive-url = https://web.archive.org/web/20100427041918/http://textbookofbacteriology.net/themicrobialworld/Polio.html | archive-date = 27 April 2010 }}</ref> In a small percentage of cases, it can spread and replicate in other sites, such as [[brown fat]], the [[reticuloendothelial]] tissues, and muscle.<ref>{{cite journal | vauthors = Sabin AB | title = Pathogenesis of poliomyelitis; reappraisal in the light of new data | journal = Science | volume = 123 | issue = 3209 | pages = 1151–57 | date = June 1956 | pmid = 13337331 | doi = 10.1126/science.123.3209.1151 | bibcode = 1956Sci...123.1151S }}</ref> This sustained replication causes a major viremia, and leads to the development of minor influenza-like symptoms. Rarely, this may progress and the virus may invade the central nervous system, provoking a local [[inflammatory response]]. In most cases, this causes a self-limiting inflammation of the [[meninges]], the layers of tissue surrounding the [[Human brain|brain]], which is known as nonparalytic aseptic meningitis.<ref name=Chamberlin_2005 /> Penetration of the CNS provides no known benefit to the virus, and is quite possibly an incidental deviation of a normal gastrointestinal infection.<ref name= Mueller>{{cite journal | vauthors = Mueller S, Wimmer E, Cello J | title = Poliovirus and poliomyelitis: a tale of guts, brains, and an accidental event | journal = Virus Research | volume = 111 | issue = 2 | pages = 175–93 | date = August 2005 | pmid = 15885840 | doi = 10.1016/j.virusres.2005.04.008 }}</ref> The mechanisms by which poliovirus spreads to the CNS are poorly understood, but it appears to be primarily a chance event&nbsp;– largely independent of the age, gender, or [[Socioeconomics|socioeconomic]] position of the individual.<ref name=Mueller />

=== Paralytic polio ===
[[File:PHIL 2767 Poliovirus Myotonic dystrophic changes.jpg|thumb|right|Denervation of [[skeletal muscle]] tissue secondary to poliovirus infection can lead to paralysis.]]
In around one percent of infections, poliovirus spreads along certain nerve fiber pathways, preferentially replicating in and destroying [[motor neuron]]s within the [[spinal cord]], [[brain stem]], or [[motor cortex]]. This leads to the development of paralytic poliomyelitis, the various forms of which (spinal, bulbar, and bulbospinal) vary only with the amount of neuronal damage and inflammation that occurs, and the region of the CNS affected.<ref>{{cite journal |last1=Punsoni |first1=Michael |last2=Lakis |first2=Nelli S. |last3=Mellion |first3=Michelle |last4=de la Monte |first4=Suzanne M. |date=June 2023 |title=Post-Polio Syndrome Revisited |journal=Neurology International |volume=15 |issue=2 |pages=569–579 |doi=10.3390/neurolint15020035 |doi-access=free |issn=2035-8377 |pmc=10123742 |pmid=37092507}}</ref>

The destruction of neuronal cells produces [[lesion]]s within the [[Dorsal root ganglion|spinal ganglia]]; these may also occur in the [[reticular formation]], [[vestibular nuclei]], [[cerebellar vermis]], and deep [[cerebellar nuclei]].<ref name=Mueller /> Inflammation associated with [[Neuron|nerve cell]] destruction often alters the color and appearance of the gray matter in the [[spinal column]], causing it to appear reddish and swollen.<ref name=Chamberlin_2005/> Other destructive changes associated with paralytic disease occur in the [[forebrain]] region, specifically the [[hypothalamus]] and [[thalamus]].<ref name=Mueller />

Early symptoms of paralytic polio include high fever, headache, stiffness in the back and neck, asymmetrical weakness of various muscles, sensitivity to touch, [[Dysphagia|difficulty swallowing]], [[Myalgia|muscle pain]], loss of superficial and deep [[reflex]]es, [[paresthesia]] (pins and needles), irritability, constipation, or difficulty urinating. Paralysis generally develops one to ten days after early symptoms begin, progresses for two to three days, and is usually complete by the time the fever breaks.<ref name= Silverstein>{{cite book |vauthors=Silverstein A, Silverstein V, Nunn LS |title=Polio |series=Diseases and People |publisher=Enslow Publishers |location=Berkeley Heights, NJ |year=2001 |isbn=978-0-7660-1592-0 |page=[https://archive.org/details/poliodiseasespeo00alvi/page/12 12] |url=https://archive.org/details/poliodiseasespeo00alvi/page/12 }}</ref>

The likelihood of developing paralytic polio increases with age, as does the extent of paralysis. In children, nonparalytic meningitis is the most likely consequence of CNS involvement, and paralysis occurs in only one in 1000 cases. In adults, paralysis occurs in one in 75 cases.<ref name="Gawne_1995">{{cite journal|year=1995|title=Post-polio syndrome: pathophysiology and clinical management|url=http://www.poliosurvivorsnetwork.org.uk/archive/lincolnshire/library/gawne/ppspandcm.html|journal=Critical Review in Physical Medicine and Rehabilitation|volume=7|issue=2|pages=147–88|vauthors=Gawne AC, Halstead LS|archive-url=https://web.archive.org/web/20160630225919/http://www.poliosurvivorsnetwork.org.uk/archive/lincolnshire/library/gawne/ppspandcm.html|archive-date=30 June 2016|access-date=30 June 2016|doi=10.1615/CritRevPhysRehabilMed.v7.i2.40|url-access=subscription}} Reproduced online with permission by Lincolnshire Post-Polio Library; retrieved on 10 November 2007.</ref> In children under five years of age, paralysis of one leg is most common; in adults, extensive paralysis of the [[chest]] and [[abdomen]] also affecting all four limbs&nbsp;– [[quadriplegia]]&nbsp;– is more likely.<ref name=Young>{{cite journal | vauthors = Young GR | title = Occupational therapy and the postpolio syndrome | journal = The American Journal of Occupational Therapy | volume = 43 | issue = 2 | pages = 97–103 | date = February 1989 | pmid = 2522741 | doi = 10.5014/ajot.43.2.97 | doi-access =  }}</ref> Paralysis rates also vary depending on the serotype of the infecting poliovirus; the highest rates of paralysis (one in 200) are associated with poliovirus type 1, the lowest rates (one in 2,000) are associated with type 2.<ref name=Nathanson>{{cite journal | vauthors = Nathanson N, Martin JR | title = The epidemiology of poliomyelitis: enigmas surrounding its appearance, epidemicity, and disappearance | journal = American Journal of Epidemiology | volume = 110 | issue = 6 | pages = 672–92 | date = December 1979 | pmid = 400274 | doi = 10.1093/oxfordjournals.aje.a112848 }}</ref>

==== Spinal polio ====
[[File:Polio spinal diagram-en.svg|thumb|left|The location of [[motor neuron]]s in the [[Anterior horn (spinal cord)|anterior horn cells]] of the [[spinal column]]]]

Spinal polio, the most common form of paralytic poliomyelitis, results from viral invasion of the motor neurons of the [[Anterior horn (spinal cord)|anterior horn cells]], or the [[ventral]] (front) [[grey matter]] section in the [[spinal column]], which are responsible for movement of the muscles, including those of the [[torso|trunk]], [[limb (anatomy)|limbs]], and the [[intercostal muscle]]s.<ref name= Henry1>{{cite book |vauthors=Frauenthal HW, Manning JV | title = Manual of infantile paralysis, with modern methods of treatment.| publisher = Philadelphia Davis | year = 1914| pages= [https://archive.org/details/amanualinfantil00fraugoog/page/n103 79]–101 |url= https://archive.org/details/amanualinfantil00fraugoog | oclc= 2078290}}</ref> Virus invasion causes inflammation of the nerve cells, leading to damage or destruction of motor neuron [[ganglion|ganglia]]. When spinal neurons die, [[Wallerian degeneration]] takes place, leading to weakness of those muscles formerly [[innervate]]d by the now-dead neurons.<ref>{{Cite web|url = http://phil.cdc.gov/phil/details.asp?pid=2760|title = A photomicrograph of the thoracic spinal cord depicting degenerative changes due to Polio Type III.|date = 18 March 2005|access-date = 24 January 2014|website = Public Health Image Library (PHIL)|publisher = Centers for Disease Control and Prevention| vauthors = Karp H |url-status = live|archive-url = https://web.archive.org/web/20140202193927/http://phil.cdc.gov/phil/details.asp?pid=2760|archive-date = 2 February 2014}}</ref> With the destruction of nerve cells, the muscles no longer receive signals from the brain or spinal cord; without nerve stimulation, the muscles [[atrophy]], becoming weak, floppy and poorly controlled, and finally completely paralyzed.<ref name=Henry1 /> Maximum paralysis progresses rapidly (two to four days), and usually involves fever and muscle pain. Deep [[tendon reflex]]es are also affected, and are typically absent or diminished; [[Sense|sensation]] (the ability to feel) in the paralyzed limbs, however, is not affected.<ref>{{cite web|url = https://www.cdc.gov/vaccines/pubs/surv-manual/chpt12-polio.html|title = Chapter 12: Poliomyelitis|date = 13 April 2013|access-date = 24 January 2014|website = Manual for the Surveillance of Vaccine-Preventable Diseases (5th Edition, 2012)|publisher = Centers for Disease Control and Prevention| vauthors = Wallace GS, Oberste SM |url-status = live|archive-url = https://web.archive.org/web/20140128113623/http://www.cdc.gov/vaccines/pubs/surv-manual/chpt12-polio.html|archive-date = 28 January 2014}}</ref>

The extent of spinal paralysis depends on the region of the cord affected, which may be [[neck|cervical]], [[human thorax|thoracic]], or [[lumbar]].<ref name=Guide>{{cite book |title=Professional Guide to Diseases (Professional Guide Series) |publisher=Lippincott Williams & Wilkins |location=Hagerstown, MD |year=2005 |pages=[https://archive.org/details/professionalguid0000unse_o7n1/page/243 243–45] |isbn=978-1-58255-370-2 |url=https://archive.org/details/professionalguid0000unse_o7n1/page/243 }}</ref> The virus may affect muscles on both sides of the body, but more often the paralysis is [[Asymmetry|asymmetrical]].<ref name=Baron /> Any [[Limb (anatomy)|limb]] or combination of limbs may be affected&nbsp;– one leg, one arm, or both legs and both arms.  Paralysis is often more severe [[Anatomical terms of location#Proximal distal|proximally]] (where the limb joins the body) than [[Anatomical terms of location#Proximal distalDistally|distally]] (the [[fingertip]]s and [[toe]]s).<ref name=Baron />

==== Bulbar polio ====
[[File:Brain bulbar region.svg|thumb|right|The location and anatomy of the bulbar region (in orange)]]
Making up about two percent of cases of paralytic polio, bulbar polio occurs when poliovirus invades and destroys nerves within the [[bulbar]] region of the [[brain stem]].<ref name = PinkBook2021 /> The bulbar region is a [[white matter]] pathway that connects the [[cerebral cortex]] to the brain stem. The destruction of these nerves weakens the muscles supplied by the [[cranial nerve]]s, producing symptoms of [[encephalitis]], and causes [[Dyspnea|difficulty breathing]], speaking and swallowing.<ref name=Late /> Critical nerves affected are the [[glossopharyngeal nerve]] (which partially controls swallowing and functions in the throat, tongue movement, and taste), the [[vagus nerve]] (which sends signals to the heart, intestines, and lungs), and the [[accessory nerve]] (which controls upper neck movement). Due to the effect on swallowing, secretions of [[mucus]] may build up in the airway, causing suffocation.<ref name = Silverstein /> Other signs and symptoms include [[facial weakness]] (caused by destruction of the [[trigeminal nerve]] and [[facial nerve]], which innervate the cheeks, [[tear duct]]s, gums, and muscles of the face, among other structures), [[diplopia|double vision]], difficulty in chewing, and abnormal [[respiratory rate]], depth, and rhythm (which may lead to [[respiratory arrest]]). [[Pulmonary edema]] and [[shock (circulatory)|shock]] are also possible and may be fatal.<ref name=Guide/>

==== Bulbospinal polio ====
Approximately 19 percent of all paralytic polio cases have both bulbar and spinal symptoms; this subtype is called respiratory or bulbospinal polio.<ref name=PinkBook2021 /> Here, the virus affects the upper part of the cervical spinal cord ([[cervical vertebrae]] C3 through C5), and paralysis of the [[Thoracic diaphragm|diaphragm]] occurs. The critical nerves affected are the [[phrenic nerve]] (which drives the diaphragm to inflate the [[human lung|lungs]]) and those that drive the muscles needed for swallowing. By destroying these nerves, this form of polio affects breathing, making it difficult or impossible for the patient to breathe without the support of a [[medical ventilator|ventilator]]. It can lead to paralysis of the arms and legs and may also affect swallowing and heart functions.<ref name= Hoyt/>

== Diagnosis ==
Paralytic poliomyelitis may be clinically suspected in individuals experiencing acute onset of flaccid paralysis in one or more limbs with decreased or absent tendon reflexes in the affected limbs that cannot be attributed to another apparent cause, and without sensory or [[cognitive]] loss.<ref>{{cite journal | title = Case definitions for infectious conditions under public health surveillance. Centers for Disease Control and Prevention | journal = MMWR. Recommendations and Reports | volume = 46 | issue = RR-10 | pages = 1–55 | date = May 1997 | pmid = 9148133 | url = ftp://ftp.cdc.gov/pub/Publications/mmwr/rr/rr4610.pdf | archive-url = https://web.archive.org/web/20070207012459/http://ftp.cdc.gov:80/pub/Publications/mmwr/rr/rr4610.pdf | archive-date = 2007-02-07 | url-status = dead | access-date = 11 November 2007 }}</ref>

A laboratory diagnosis is usually made based on the recovery of poliovirus from a stool sample or a swab of the [[human pharynx|pharynx]]. Rarely, it may be possible to identify poliovirus  in the blood or in the  [[cerebrospinal fluid]]. Poliovirus samples are further analysed using [[reverse transcription polymerase chain reaction]] (RT-PCR) or [[DNA sequencing|genomic sequencing]] to determine the serotype (i.e., 1, 2, or 3), and whether the virus is a wild or vaccine-derived strain.<ref name = PinkBook2021/>

== Prevention ==
=== Passive immunization ===
In 1950, [[William Hammon]] at the [[University of Pittsburgh]] purified the [[gamma globulin]] component of the [[blood plasma]] of polio survivors.<ref name=Hammon_1955>{{cite journal | vauthors = Hammon WM | title = Passive immunization against poliomyelitis | journal = Monograph Series. World Health Organization | volume = 26 | pages = 357–70 | year = 1955 | pmid = 14374581 }}</ref> Hammon proposed the gamma globulin, which contained antibodies to poliovirus, could be used to halt poliovirus infection, prevent disease, and reduce the severity of disease in other patients who had contracted polio. The results of a large [[clinical trial]] were promising; the gamma globulin was shown to be about 80 percent effective in preventing the development of paralytic poliomyelitis.<ref>{{cite journal | vauthors = Hammon WM, Coriell LL, Ludwig EH, McAllister RM, Greene AE, Sather GE, Wehrle PF | title = Evaluation of Red Cross gamma globulin as a prophylactic agent for poliomyelitis. 5. Reanalysis of results based on laboratory-confirmed cases | journal = Journal of the American Medical Association | volume = 156 | issue = 1 | pages = 21–27 | date = September 1954 | pmid = 13183798 | doi = 10.1001/jama.1954.02950010023009 }}</ref> It was also shown to reduce the severity of the disease in patients who developed polio.<ref name=Hammon_1955 /> Due to the limited supply of blood plasma gamma globulin was later deemed impractical for widespread use and the medical community focused on the development of a polio vaccine.<ref name=Rinaldo>{{cite journal | vauthors = Rinaldo CR | title = Passive immunization against poliomyelitis: the Hammon gamma globulin field trials, 1951–1953 | journal = American Journal of Public Health | volume = 95 | issue = 5 | pages = 790–99 | date = May 2005 | pmid = 15855454 | pmc = 1449257 | doi = 10.2105/AJPH.2004.040790 }}</ref>

=== Vaccine ===
{{Main|Polio vaccine}}
[[File:Poliodrops.jpg|thumb|right|A child receiving an oral polio vaccine]]

Two types of vaccine are used throughout the world to combat polio: an [[Inactivated vaccine|inactivated]] poliovirus given by injection, and a [[Attenuated vaccine|weakened]] poliovirus given by mouth. Both types induce immunity to polio and are effective in protecting individuals from disease.<ref name="WHO20162">{{cite journal |vauthors=((World Health Organization)) |date=2016 |title=Polio vaccines: WHO position paper – March, 2016 |journal=Weekly Epidemiological Record |volume=91 |issue=12 |pages=145–68 |pmid=27039410 |hdl-access=free |hdl=10665/254399}}</ref>

The inactivated polio vaccine (IPV) was developed in 1952 by [[Jonas Salk]] at the University of Pittsburgh, and announced to the world on 12 April 1955.<ref name="Spice">{{cite news | vauthors = Spice B |title=Tireless polio research effort bears fruit and indignation |url=http://www.post-gazette.com/pg/05094/482468.stm |work=The Salk vaccine: 50 years later/ second of two parts |publisher=[[Pittsburgh Post-Gazette]] |date=4 April 2005 |access-date=23 August 2008 |url-status=live |archive-url=https://web.archive.org/web/20080905022100/http://www.post-gazette.com/pg/05094/482468.stm |archive-date=5 September 2008 }}</ref> The Salk vaccine is based on poliovirus grown in a type of monkey kidney [[tissue culture]] ([[vero cell]] [[cell culture|line]]), which is chemically inactivated with [[formalin]].<ref name="Kew_2005" /> After two doses of IPV (given by [[injection (medicine)|injection]]), 90 percent or more of individuals develop protective antibody to all three [[serotype]]s of poliovirus, and at least 99 percent are immune to poliovirus following three doses.<ref name="PinkBook2021" />

Subsequently, [[Albert Sabin]] developed a polio vaccine that can be administered orally (oral polio vaccine - OPV), comprising a live, [[Attenuated vaccine|attenuated]] virus. It was produced by the repeated passage of the virus through nonhuman cells at sub[[physiological]] temperatures.<ref name="Sabin_1973">{{cite journal |vauthors=Sabin AB, Boulger LR | title = History of Sabin attenuated poliovirus oral live vaccine strains | journal = Journal of Biological Standardization | year = 1973 | volume = 1 | pages = 115–18 |doi=10.1016/0092-1157(73)90048-6 | issue = 2}}</ref> The attenuated poliovirus in the Sabin vaccine replicates very efficiently in the gut, the primary site of wild poliovirus infection and replication, but the vaccine strain is unable to replicate efficiently within [[nervous system]] tissue.<ref>{{cite journal | vauthors = Sabin AB, Ramos-Alvarez M, Alvarez-Amezquita J, et al | title = Live, orally given poliovirus vaccine. Effects of rapid mass immunization on population under conditions of massive enteric infection with other viruses | journal = JAMA | volume = 173 | issue = 14 | pages = 1521–26 | date = August 1960 | pmid = 14440553 | doi = 10.1001/jama.1960.03020320001001 }}</ref> A single dose of Sabin's trivalent OPV produces immunity to all three poliovirus serotypes in about 50 percent of recipients. Three doses of OPV produce protective antibody to all three poliovirus types in more than 95 percent of recipients.<ref name="PinkBook2021" /> [[Clinical trial|Human trials]] of Sabin's vaccine began in 1957,<ref name="ScienceOdyssey">{{cite web | title = A Science Odyssey: People and Discoveries | publisher = PBS | year = 1998 | url = https://www.pbs.org/wgbh/aso/databank/entries/dm52sa.html | access-date = 23 August 2008 | url-status = live | archive-url = https://web.archive.org/web/20080726075448/http://www.pbs.org/wgbh/aso/databank/entries/dm52sa.html | archive-date = 26 July 2008  }}</ref> and in 1958, it was selected, in competition with the live attenuated vaccines of [[Hilary Koprowski|Koprowski]] and other researchers, by the US National Institutes of Health.<ref name="Sanofi">{{cite web |title=Polio Vaccine &#124; IPV Vaccine |url=http://www.polio.info/polio-eradication/front/templates/index.jsp?siteCode=POLIO&codeRubrique=34&lang=EN |archive-url=https://web.archive.org/web/20071007095443/http://www.polio.info/polio-eradication/front/templates/index.jsp?siteCode=POLIO&codeRubrique=34&lang=EN |archive-date=7 October 2007 |access-date=1 November 2011}} Accessed 16 December 2009.</ref> Licensed in 1962,<ref name="ScienceOdyssey" /> it rapidly became the only oral polio vaccine used worldwide.<ref name="Sanofi" />

OPV efficiently blocks person-to-person transmission of wild poliovirus by oral–oral and fecal–oral routes, thereby protecting both individual vaccine recipients and the wider community. The live attenuated virus may be transmitted from vaccinees to their unvaccinated contacts, resulting in wider community immunity.<ref name="Fine2">{{cite journal |vauthors=Fine PE, Carneiro IA |date=November 1999 |title=Transmissibility and persistence of oral polio vaccine viruses: implications for the global poliomyelitis eradication initiative |journal=American Journal of Epidemiology |volume=150 |issue=10 |pages=1001–21 |doi=10.1093/oxfordjournals.aje.a009924 |pmid=10568615 |doi-access=free}}</ref> IPV confers good immunity but is less effective at preventing spread of wild poliovirus by the fecal–oral route.<ref>{{Cite journal |last1=Alfaro-Murillo |first1=Jorge A. |last2=Ávila-Agüero |first2=María L. |last3=Fitzpatrick |first3=Meagan C. |last4=Crystal |first4=Caroline J. |last5=Falleiros-Arlant |first5=Luiza-Helena |last6=Galvani |first6=Alison P. |date=2020-04-04 |title=The case for replacing the live oral polio vaccine with the inactivated vaccine throughout the Americas |journal=Lancet |volume=395 |issue=10230 |pages=1163–1166 |doi=10.1016/S0140-6736(20)30213-0 |issn=0140-6736 |pmc=8572547 |pmid=32247397}}</ref>
[[File:Number of polio cases since 2000.svg|thumb|Wild polio and cVDPV cases (2000–2024).]]
Because the oral polio vaccine is inexpensive, easy to administer, and produces excellent immunity in the intestine (which helps prevent infection with wild virus in areas where it is [[Endemic (epidemiology)|endemic]]), it has been the vaccine of choice for controlling poliomyelitis in many countries.<ref name="Peds">{{cite journal |title=Poliomyelitis prevention: recommendations for use of inactivated poliovirus vaccine and live oral poliovirus vaccine. American Academy of Pediatrics Committee on Infectious Diseases |journal=Pediatrics |volume=99 |issue=2 |pages=300–305 |date=February 1997 |pmid=9024465 |doi=10.1542/peds.99.2.300 |doi-access=free}}</ref> On very rare occasions, the attenuated virus in the Sabin OPV can revert into a form that can paralyze.<ref>{{cite web |date=9 April 2024 |title=GPEI-Variant Polio (cVDPV) Cases |url=https://polioeradication.org/this-week/variant-polio-cvdpv-cases/ |access-date=2024-04-15 |website=Global Polio Eradication Initiative – World Health Organization |language=en-GB}}</ref> In 2017, cases caused by vaccine-derived poliovirus (cVDPV) outnumbered wild poliovirus cases for the first time, due to wild polio cases hitting record lows.<ref>{{cite web |last=Kunasekaran |first=Mohana |title=Eradication of polio – Is Syria being left behind? |url=https://sphcm.med.unsw.edu.au/infectious-diseases-blog/eradication-polio-syria-being-left-behind |publisher=School of Public Health and Community Medicine |date=16 May 2017 |access-date=27 September 2022 |archive-url=https://web.archive.org/web/20181006114450/https://sphcm.med.unsw.edu.au/infectious-diseases-blog/eradication-polio-syria-being-left-behind |archive-date=6 October 2018}}</ref> Most [[Developed country|industrialized countries]] have switched to inactivated polio vaccine, which cannot revert, either as the sole vaccine against poliomyelitis or in combination with oral polio vaccine.<ref>{{cite web |url=https://www.who.int/ith/vaccines/2007_routine_use/en/index11.html |title=WHO: Vaccines for routine use |access-date=23 August 2008 |page=12 |work=International travel and health |archive-url=https://web.archive.org/web/20080606170542/http://www.who.int/ith/vaccines/2007_routine_use/en/index11.html |archive-date=6 June 2008}}</ref>

An improved oral vaccine (Novel oral polio vaccine type 2 - nOPV2) began development in 2011 and was granted emergency licensing in 2021, and subsequently full licensure in December 2023.<ref name=":2">{{cite web |date=12 April 2024 |title=GPEI-OPV Oral polio vaccine |url=https://polioeradication.org/polio-today/polio-prevention/the-vaccines/opv/ |access-date=12 April 2024 |website=Global Polio Eradication Initiative - World Health Organization |language=en-GB}}</ref> This has greater genetic stability than the traditional oral vaccine and is less likely to revert to a virulent form.<ref name=":2" />

== Treatment ==
There is no [[cure]] for polio, but there are treatments. The focus of modern treatment has been on providing relief of symptoms, speeding recovery and preventing complications. Supportive measures include [[antibiotics]] to prevent infections in weakened muscles, [[analgesics]] for pain, moderate exercise and a nutritious diet.<ref name=Daniel>{{cite book | vauthors = Daniel TM, Robbins FC |title=Polio |publisher=University of Rochester Press |location=Rochester, NY |year=1997 |pages=8–10 |isbn=978-1-58046-066-8}}</ref> Treatment of polio often requires long-term rehabilitation, including [[occupational therapy]], [[physical therapy]], braces, corrective shoes and, in some cases, [[orthopedic surgery]].<ref name=Guide />

Portable [[ventilator]]s may be required to support breathing. Historically, a noninvasive, negative-pressure ventilator, more commonly called an [[iron lung]], was used to artificially maintain respiration during an acute polio infection until a person could breathe independently (generally about one to two weeks). The use of iron lungs is largely obsolete in modern medicine as more modern breathing therapies have been developed<ref>{{Cite journal |last1=Corrado |first1=A. |last2=Ginanni |first2=R. |last3=Villella |first3=G. |last4=Gorini |first4=M. |last5=Augustynen |first5=A. |last6=Tozzi |first6=D. |last7=Peris |first7=A. |last8=Grifoni |first8=S. |last9=Messori |first9=A. |last10=Nozzoli |first10=C. |last11=Berni |first11=G. |date=March 2004 |title=Iron lung versus conventional mechanical ventilation in acute exacerbation of COPD |journal=The European Respiratory Journal |volume=23 |issue=3 |pages=419–24 |doi=10.1183/09031936.04.00029304 |issn=0903-1936 |pmid=15065832 |doi-access=free}}</ref> and due to the [[Polio eradication|eradication of polio]] in most of the world.<ref name="americas_last_2017_11_22_independent_co_uk">{{cite web |last=Buncombe |first=Andrew |date=November 22, 2017 |title=America's last iron lung users on their lives spent inside obsolete ventilators |url=https://www.independent.co.uk/news/world/americas/polio-iron-lung-survivors-photos-lives-inside-ventilators-a8070881.html |url-status=live |archive-url=https://ghostarchive.org/archive/20220525/https://www.independent.co.uk/news/world/americas/polio-iron-lung-survivors-photos-lives-inside-ventilators-a8070881.html |archive-date=May 25, 2022 |access-date=April 16, 2019 |work=[[The Independent]]}}</ref>

Other [[History of poliomyelitis#Historical treatments|historical treatments for polio]] include [[hydrotherapy]], [[electrotherapy]], massage and passive motion exercises, and surgical treatments, such as tendon lengthening and nerve grafting.<ref name=Henry1 />

== Prognosis ==
[[File:Polio sequelle.jpg|thumb|A girl with [[genu recurvatum]] of her right leg due to polio]]
Patients with abortive polio infections recover completely. In those who develop only aseptic meningitis, the symptoms can be expected to persist for two to ten days, followed by complete recovery.<ref name=Neumann/> In cases of spinal polio, if the affected nerve cells are completely destroyed, paralysis will be permanent; cells that are not destroyed, but lose function temporarily, may recover within four to six weeks after onset.<ref name=Neumann>{{cite journal | vauthors = Neumann DA | title = Polio: its impact on the people of the United States and the emerging profession of physical therapy | journal = The Journal of Orthopaedic and Sports Physical Therapy | volume = 34 | issue = 8 | pages = 479–92 | date = August 2004 | pmid = 15373011 | doi = 10.2519/jospt.2004.0301 | url = http://www.post-polio.org/edu/hpros/Aug04HistPersNeumann.pdf | url-status = live | archive-url = https://web.archive.org/web/20080910165631/http://www.post-polio.org/edu/hpros/Aug04HistPersNeumann.pdf | archive-date = 10 September 2008 }} Reproduced online with permission by Post-Polio Health International; retrieved on 10 November 2007.</ref> Half the patients with spinal polio recover fully; one-quarter recover with mild disability, and the remaining quarter are left with severe disability.<ref>{{cite book | vauthors = Cuccurullo SJ |title=Physical Medicine and Rehabilitation Board Review |url=https://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=physmedrehab.table.8357 |archive-url=https://web.archive.org/web/20071012215404/http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=physmedrehab.table.8357 |archive-date=12 October 2007 |publisher=Demos Medical Publishing |year=2004 |isbn=978-1-888799-45-3}}</ref> The degree of both acute paralysis and residual paralysis is likely to be proportional to the degree of [[viremia]], and [[inversely proportional]] to the degree of [[immunity (medical)|immunity]].<ref name= Mueller/> Spinal polio is rarely fatal.<ref name=Silverstein />

Without respiratory support, consequences of poliomyelitis with [[Respiration (physiology)|respiratory]] involvement include [[suffocation]] or [[aspiration pneumonia|pneumonia from aspiration of secretions]].<ref name= Goldberg>{{cite journal | vauthors = Goldberg AI | title = Noninvasive mechanical ventilation at home: building upon the tradition | journal = Chest | volume = 121 | issue = 2 | pages = 321–24 | date = February 2002 | pmid = 11834636 | doi = 10.1378/chest.121.2.321 | doi-access = free }}</ref> Overall, 5 to 10 percent of patients with paralytic polio die due to the paralysis of muscles used for breathing. The [[case fatality rate]] (CFR) varies by age: 2 to 5 percent of children and up to 15 to 30 percent of adults die.<ref name=PinkBook2021 /> Bulbar polio often causes death if respiratory support is not provided;<ref name= Hoyt /> with support, its CFR ranges from 25 to 75 percent, depending on the age of the patient.<ref name=PinkBook2021 /><ref>{{cite journal | vauthors = Miller AH, Buck LS | title = Tracheotomy in bulbar poliomyelitis | journal = California Medicine | volume = 72 | issue = 1 | pages = 34–36 | date = January 1950 | pmid = 15398892 | pmc = 1520308 }}</ref> When intermittent positive pressure ventilation is available, the fatalities can be reduced to 15 percent.<ref name=Wackers>{{cite thesis| author = Wackers, G.| title = Constructivist Medicine| type = PhD thesis| publisher = Maastricht: Universitaire Pers Maastricht| year = 1994| url = http://www.fdcw.unimaas.nl/personal/WebSitesMWT/Wackers/proefschrift.html#h4| access-date = 4 January 2008| archive-url = https://web.archive.org/web/20071223223131/http://www.fdcw.unimaas.nl/personal/WebSitesMWT/Wackers/proefschrift.html#h4| archive-date = 23 December 2007}}</ref>

=== Recovery ===
Many cases of poliomyelitis result in only temporary paralysis.<ref name=Henry1 /> Generally in these cases, nerve impulses return to the paralyzed muscle within a month, and recovery is complete in six to eight months.<ref name=Neumann /> The [[neurophysiology|neurophysiological]] processes involved in recovery following acute paralytic poliomyelitis are quite effective; muscles are able to retain normal strength even if half the original motor neurons have been lost.<ref>{{cite journal | vauthors = Sandberg A, Hansson B, Stålberg E | title = Comparison between concentric needle EMG and macro EMG in patients with a history of polio | journal = Clinical Neurophysiology | volume = 110 | issue = 11 | pages = 1900–08 | date = November 1999 | pmid = 10576485 | doi = 10.1016/S1388-2457(99)00150-9 | s2cid = 14534071 }}</ref> Paralysis remaining after one year is likely to be permanent, although some recovery of muscle strength is possible up to 18 months after infection.<ref name=Neumann />

One mechanism involved in recovery is nerve terminal sprouting, in which remaining brainstem and spinal cord motor neurons develop new branches, or axonal sprouts.<ref>{{cite journal | vauthors = Cashman NR, Covault J, Wollman RL, Sanes JR | title = Neural cell adhesion molecule in normal, denervated, and myopathic human muscle | journal = Annals of Neurology | volume = 21 | issue = 5 | pages = 481–89 | date = May 1987 | pmid = 3296947 | doi = 10.1002/ana.410210512 | s2cid = 13102779 }}</ref> These sprouts can [[reinnervate]] orphaned muscle fibers that have been denervated by acute polio infection,<ref name=Agre>{{cite journal | vauthors = Agre JC, Rodríquez AA, Tafel JA | title = Late effects of polio: critical review of the literature on neuromuscular function | journal = Archives of Physical Medicine and Rehabilitation | volume = 72 | issue = 11 | pages = 923–31 | date = October 1991 | pmid = 1929813 | doi = 10.1016/0003-9993(91)90013-9 }}</ref> restoring the fibers' capacity to contract and improving strength.<ref name="Cashman"/> Terminal sprouting may generate a few significantly enlarged motor neurons doing work previously performed by as many as four or five units:<ref name=Gawne_1995 /> a single motor neuron that once controlled 200 muscle cells might control 800 to 1000 cells. Other mechanisms that occur during the rehabilitation phase, and contribute to muscle strength restoration, include [[muscle hypertrophy|myofiber hypertrophy]]&nbsp;– enlargement of muscle fibers through exercise and activity&nbsp;– and transformation of [[Muscle fiber#Type II|type II muscle fibers]] to [[Muscle fiber#Type I|type I muscle fibers]].<ref name=Agre /><ref name = Grimby_1989>{{cite journal | vauthors = Grimby G, Einarsson G, Hedberg M, Aniansson A | title = Muscle adaptive changes in post-polio subjects | journal = Scandinavian Journal of Rehabilitation Medicine | volume = 21 | issue = 1 | pages = 19–26 | year = 1989 | doi = 10.2340/165019779891926 | doi-broken-date = 8 July 2025 | pmid = 2711135 | s2cid = 9440972 | doi-access = free }}</ref>

In addition to these physiological processes, the body can compensate for residual paralysis in other ways. Weaker muscles can be used at a higher than usual intensity relative to the [[Muscle contraction#Types|muscle's maximal capacity]], little-used muscles can be developed, and [[ligament]]s can enable stability and mobility.<ref name = Grimby_1989 />

===Complications===
Residual complications of paralytic polio often occur following the initial recovery process.<ref name= Late /> Muscle [[paresis]] and paralysis can sometimes result in [[skeletal]] deformities, tightening of the joints, and movement disability. Once the muscles in the limb become flaccid, they may interfere with the function of other muscles. A typical manifestation of this problem is [[equinus foot]] (similar to [[club foot]]). This deformity develops when the muscles that pull the toes downward are working, but those that pull it upward are not, and the foot naturally tends to drop toward the ground. If the problem is left untreated, the [[Achilles tendon]]s at the back of the foot retract and the foot cannot take on a normal position. People with polio that develop equinus foot cannot walk properly because they cannot put their heels on the ground. A similar situation can develop if the arms become paralyzed.<ref name= Aftereffects>{{cite web | publisher = Sanofi Pasteur | title = Poliomyelitis virus (picornavirus, enterovirus), after-effects of the polio, paralysis, deformations | work = Polio Eradication | url = http://www.polio.info/polio-eradication/front/index.jsp?siteCode=POLIO&lang=EN&codeRubrique=14 | access-date = 23 August 2008|archive-url = https://web.archive.org/web/20071007100336/http://www.polio.info/polio-eradication/front/index.jsp?siteCode=POLIO&lang=EN&codeRubrique=14 |archive-date = 7 October 2007}}</ref>

In some cases the growth of an affected leg is slowed by polio, while the other leg continues to grow normally. The result is that one leg is shorter than the other and the person limps and leans to one side, in turn leading to deformities of the spine (such as [[scoliosis]]).<ref name= Aftereffects /> [[Osteoporosis]] and increased likelihood of [[bone fracture]]s may occur. An intervention to prevent or lessen length disparity can be to perform an [[epiphysiodesis]] on the distal femoral and proximal tibial/fibular condyles, so that limb's growth is artificially stunted, and by the time of [[epiphyseal plate|epiphyseal (growth) plate]] closure, the legs are more equal in length. Alternatively, a person can be fitted with custom-made footwear which corrects the difference in leg lengths. Other surgery to re-balance muscular agonist/antagonist imbalances may also be helpful.  Extended use of braces or wheelchairs may cause [[nerve compression syndrome|compression neuropathy]], as well as a loss of proper function of the [[vein]]s in the legs, due to pooling of blood in paralyzed lower limbs.<ref name= Hoyt>{{cite book | vauthors = Hoyt WG, Miller N, Walsh F |title=Walsh and Hoyt's clinical neuro-ophthalmology |publisher=Lippincott Williams & Wilkins |location=Hagerstown, MD |year=2005 |pages=3264–65 |isbn=978-0-7817-4814-8 }}</ref><ref name=MayoComps>{{cite web| author = Mayo Clinic Staff| date = 19 May 2005| url = http://www.mayoclinic.com/health/polio/DS00572/DSECTION=complications| title = Polio: Complications| publisher = Mayo Foundation for Medical Education and Research (MFMER)| access-date = 26 February 2007| url-status = live| archive-url = https://web.archive.org/web/20080623225045/http://www.mayoclinic.com/health/polio/DS00572/DSECTION%3Dcomplications| archive-date = 23 June 2008}}</ref> Complications from prolonged immobility involving the [[lungs]], [[kidney]]s and [[heart]] include [[pulmonary edema]], [[aspiration pneumonia]], [[urinary tract infection]]s, [[kidney stone]]s, [[paralytic ileus]], [[myocarditis]] and [[cor pulmonale]].<ref name= Hoyt/><ref name=MayoComps />

===Post-polio syndrome===
{{Main|Post-polio syndrome}}
Between 25 percent and 50 percent of individuals who have recovered from paralytic polio in childhood can develop additional symptoms decades after recovering from the acute infection,<ref name="NINDS Post-Polio Syndrome Fact Sheet">{{cite web |url=http://www.ninds.nih.gov/disorders/post_polio/detail_post_polio.htm |title=Post-Polio Syndrome Fact Sheet: National Institute of Neurological Disorders and Stroke (NINDS) |access-date=2 August 2011 |archive-url=https://web.archive.org/web/20110729090555/http://www.ninds.nih.gov/disorders/post_polio/detail_post_polio.htm |archive-date=29 July 2011 }}</ref> notably new muscle weakness and extreme fatigue. This condition is known as [[post-polio syndrome]] (PPS) or post-polio sequelae.<ref name=Cashman>{{cite journal | vauthors = Trojan DA, Cashman NR | title = Post-poliomyelitis syndrome | journal = Muscle & Nerve | volume = 31 | issue = 1 | pages = 6–19 | date = January 2005 | pmid = 15599928 | doi = 10.1002/mus.20259 | s2cid = 25442322 }}</ref> The symptoms of PPS are thought to involve a failure of the oversized [[motor unit]]s created during the recovery phase of the paralytic disease.<ref name=Ramlow_1992>{{cite journal | vauthors = Ramlow J, Alexander M, LaPorte R, Kaufmann C, [[Lewis Kuller|Kuller L]] | title = Epidemiology of the post-polio syndrome | journal = American Journal of Epidemiology | volume = 136 | issue = 7 | pages = 769–86 | date = October 1992 | pmid = 1442743 | doi = 10.1093/aje/136.7.769 }}</ref><ref name=Annals>{{cite journal | vauthors = Lin KH, Lim YW | title = Post-poliomyelitis syndrome: case report and review of the literature | journal = Annals of the Academy of Medicine, Singapore | volume = 34 | issue = 7 | pages = 447–49 | date = August 2005 | doi = 10.47102/annals-acadmedsg.V34N7p447 | pmid = 16123820 | url = http://www.annals.edu.sg/pdf/34VolNo7200508/V34N7p447.pdf | url-status = live | archive-url = https://web.archive.org/web/20070307110123/http://www.annals.edu.sg/pdf/34VolNo7200508/V34N7p447.pdf | archive-date = 7 March 2007 }}</ref> Contributing factors that increase the risk of PPS include aging with loss of neuron units, the presence of a permanent residual impairment after recovery from the acute illness, and both overuse and disuse of neurons. PPS is a slow, progressive disease, and there is no specific treatment for it.<ref name=Cashman /> Post-polio syndrome is not an infectious process, and persons experiencing the syndrome do not shed poliovirus.<ref name=PinkBook2021 />

== Orthotics ==
[[File:Orthese am Poliobein.jpg|thumb|[[Orthotics|Orthosis]] with stance phase control knee joint]]
Paralysis, length differences and deformations of the lower extremities can lead to a hindrance when walking with compensation mechanisms that lead to a severe impairment of the gait pattern. In order to be able to stand and walk safely and to improve the gait pattern, [[orthotics]] can be included in the therapy concept. Today, modern materials and functional elements enable the orthosis to be specifically adapted to the requirements resulting from the patient's gait. Mechanical stance phase control knee joints may secure the knee joint in the early stance phases and release again for knee flexion when the swing phase is initiated. With the help of an orthotic treatment with a stance phase control knee joint, a natural gait pattern can be achieved despite mechanical protection against unwanted knee flexion. In these cases, locked knee joints are often used, which have a good safety function, but do not allow knee flexion when walking during swing phase. With such joints, the knee joint remains mechanically blocked during the swing phase. Patients with locked knee joints must swing the leg forward with the knee extended even during the swing phase. This only works if the patient develops compensatory mechanisms, e.g. by raising the body's center of gravity in the swing phase (Duchenne limping) or by swinging the orthotic leg to the side (circumduction).<ref>{{Cite book|url=https://musculoskeletalkey.com/orthoses-for-persons-with-postpolio-syndrome/|title=Orthoses for persons with postpolio syndrome.|publisher=Mosby/Elsevier|year=2008|isbn=978-0-323-03931-4|veditors=Hsu JD, Michael J, Fisk J|series=AAOS Atlas of Orthoses and Assistive Devices|location=Philadelphia|pages=411–17|oclc=152793635 |access-date=20 July 2021|archive-date=13 June 2021|archive-url=https://web.archive.org/web/20210613195026/https://musculoskeletalkey.com/orthoses-for-persons-with-postpolio-syndrome/|url-status=live}}</ref><ref>{{cite journal | vauthors = Irby SE, Bernhardt KA, Kaufman KR | title = Gait of stance control orthosis users: the dynamic knee brace system | journal = Prosthetics and Orthotics International | volume = 29 | issue = 3 | pages = 269–82 | date = December 2005 | pmid = 16466156 | doi = 10.1080/03093640500238915 | s2cid = 7166949 }}</ref><ref>{{cite journal | vauthors = Brehm MA, Beelen A, Doorenbosch CA, Harlaar J, Nollet F | title = Effect of carbon-composite knee-ankle-foot orthoses on walking efficiency and gait in former polio patients | journal = Journal of Rehabilitation Medicine | volume = 39 | issue = 8 | pages = 651–7 | date = October 2007 | pmid = 17896058 | doi = 10.2340/16501977-0110 | doi-access = free }}</ref>

==Epidemiology==
Major polio [[epidemic]]s were unknown before the 20th century; up until that time, polio was an endemic disease worldwide.<ref name="Trevelyan_2005">{{cite journal |vauthors=Trevelyan B, Smallman-Raynor M, Cliff A |year=2005 |title=The Spatial Dynamics of Poliomyelitis in the United States: From Epidemic Emergence to Vaccine-Induced Retreat, 1910–1971 |journal=Ann Assoc Am Geogr |volume=95 |issue=2 |pages=269–293 |doi=10.1111/j.1467-8306.2005.00460.x |pmc=1473032 |pmid=16741562|bibcode=2005AAAG...95..269T }}</ref> Mothers who had survived polio infection passed on temporary immunity to their babies in the womb and through breast milk.<ref name="Baron2">{{cite book |url=https://www.ncbi.nlm.nih.gov/books/NBK7687/ |title=Picornaviruses: The Enteroviruses: Polioviruses ''in:'' Baron's Medical Microbiology |vauthors=Yin-Murphy M, Almond JW |publisher=University of Texas Medical Branch |year=1996 |isbn=0-9631172-1-1 |editor=Baron S |edition=4th |chapter=Picornaviruses |pmid=21413259 |display-editors=etal |archive-url=https://web.archive.org/web/20081207154734/http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=mmed.section.2862 |archive-date=2008-12-07 |url-status=live}}</ref> As a result, an infant who encountered a polio infection generally suffered only mild symptoms and acquired a long-term immunity to the disease.<ref name=":0">{{cite web |title=Polio: a 20th century epidemic {{!}} Science Museum |url=https://www.sciencemuseum.org.uk/objects-and-stories/medicine/polio-20th-century-epidemic |access-date=2024-04-12 |website=www.sciencemuseum.org.uk}}</ref> With improvements in sanitation and hygiene during the 19th century, the general level of [[herd immunity]] in the population declined; this provided circumstances where [[epidemic]]s of polio became frequent.<ref name=":0" /> It is estimated that epidemic polio killed or paralysed over half a million people every year.<ref>{{cite web |title=History of polio vaccination |url=https://www.who.int/news-room/spotlight/history-of-vaccination/history-of-polio-vaccination |access-date=2024-04-10 |website=World health Organization}}</ref>

Following the widespread use of poliovirus vaccine in the mid-1950s, new cases of poliomyelitis declined dramatically in many industrialized countries.<ref name="Hinman">{{cite journal |author=Hinman A |year=1984 |title=Landmark perspective: Mass vaccination against polio |journal=JAMA |volume=251 |issue=22 |pages=2994–6 |doi=10.1001/jama.1984.03340460072029 |pmid=6371280}}</ref> Efforts to completely eradicate the disease started in 1988 and are ongoing.<ref name=":1" />

===Circulating vaccine-derived polioviruses===
The [[oral polio vaccine]], while highly effective, has the disadvantage that it contains a live virus which has been [[Attenuated vaccine|attenuated]] so that it cannot cause severe illness. The vaccine virus is excreted in the stool, and in under-immunized communities it can spread from person to person. This is known as '''circulating vaccine-derived poliovirus''' (cVDPV) or more simply as '''variant poliovirus'''.<ref name="www.cdc.gov2022" /><ref>{{cite web |title=GPEI-Variant Poliovirus (cVDPV) |url=https://polioeradication.org/polio-today/polio-prevention/the-virus/variant-poliovirus-cvdpv/ |access-date=2024-08-07 |website=Global Polio Eradication Initiative |language=en-GB}}</ref>

With prolonged transmission of this kind, the weakened virus can mutate and revert to a form that causes illness and paralysis. Cases of cVDPV now exceed wild-type cases, making it desirable to discontinue the use of the oral polio vaccine as soon as safely possible and instead use other types of polio vaccines.<ref name="www.cdc.gov2022" /><ref>{{cite web |title=GPEI-Vaccine-Derived Polioviruses |url=https://polioeradication.org/polio-today/polio-prevention/the-virus/vaccine-derived-polio-viruses/ |access-date=2022-09-03 |archive-date=28 August 2022 |archive-url=https://web.archive.org/web/20220828160534/https://polioeradication.org/polio-today/polio-prevention/the-virus/vaccine-derived-polio-viruses/ |url-status=live }}</ref>

===Eradication===
{{see also|Poliomyelitis eradication}}
[[File:The-decade-of-the-last-recorded-case-of-paralytic-polio-by-country-2023.png|thumb|The decade of the last recorded case of paralytic polio.<ref>{{cite web |title=The decade of the last recorded case of paralytic polio by country |url=https://ourworldindata.org/grapher/the-decade-of-the-last-recorded-case-of-paralytic-polio-by-country |website=Our World in Data |access-date=4 March 2020 |archive-date=13 May 2020 |archive-url=https://web.archive.org/web/20200513120540/https://ourworldindata.org/grapher/the-decade-of-the-last-recorded-case-of-paralytic-polio-by-country |url-status=live }}</ref>]]
A global effort to [[Eradication of infectious disease|eradicate]] polio – the [[Global Polio Eradication Initiative]] – began in 1988, led by the [[World Health Organization]], [[UNICEF]], and [[The Rotary Foundation]].<ref name=":1">{{cite web| vauthors = Vaught M |title=Polio Vaccine Celebrates 60th Anniversary|url=https://www.rotary.org/en/polio-vaccine-celebrates-60th-anniversary|website=Rotary International|access-date=11 November 2015|date=10 April 2015|archive-url=https://web.archive.org/web/20151117023228/https://www.rotary.org/en/polio-vaccine-celebrates-60th-anniversary|archive-date=17 November 2015}}</ref> Polio is one of only two diseases currently the subject of a global [[eradication of infectious diseases|eradication program]], the other being [[Guinea worm disease]].<ref>{{cite web| vauthors = Akst J |title=Driven to Extinction|url=http://www.the-scientist.com/?articles.view/articleNo/43382/title/Driven-to-Extinction/|website=The Scientist|access-date=11 November 2015|date=1 July 2015|url-status=live|archive-url=https://web.archive.org/web/20151118224852/http://www.the-scientist.com/?articles.view%2FarticleNo%2F43382%2Ftitle%2FDriven-to-Extinction%2F|archive-date=18 November 2015}}</ref> So far, the only diseases completely eradicated by humankind are [[smallpox]], declared eradicated in 1980,<ref name="WHO_smallpox">{{cite web|title=Smallpox |work=WHO Factsheet |url=https://www.who.int/mediacentre/factsheets/smallpox/en/ |access-date=23 August 2008 |archive-url=https://web.archive.org/web/20070921235036/http://www.who.int/mediacentre/factsheets/smallpox/en/ |archive-date=21 September 2007}}</ref><ref>{{cite web|title=The Smallpox Eradication Programme – SEP (1966–1980)|url=https://www.who.int/features/2010/smallpox/en/|website=WHO|access-date=11 November 2015|archive-url=https://web.archive.org/web/20151109123858/http://www.who.int/features/2010/smallpox/en/|archive-date=9 November 2015}}</ref> and [[rinderpest]], declared eradicated in 2011.<ref>{{cite press release|title=No more deaths from rinderpest|url=http://www.oie.int/for-the-media/press-releases/detail/article/no-more-deaths-from-rinderpest/|publisher=[[World Organisation for Animal Health]]|access-date=11 November 2015|date=25 May 2011|archive-url=https://web.archive.org/web/20150924072257/http://www.oie.int/for-the-media/press-releases/detail/article/no-more-deaths-from-rinderpest/|archive-date=24 September 2015}}</ref> In April 2012, the World Health Assembly declared that the failure to completely eradicate polio would be a programmatic emergency for global public health, and that it "must not happen".<ref>{{cite book |author=World Health Assembly |year=2012 |title=Poliomyelitis: intensification of the global eradication initiative. Agenda item A65/20 |url=http://apps.who.int/gb/ebwha/pdf_files/wha65/A65_20-en.pdf |location=Geneva, Switzerland |publisher=World Health Organization |access-date=7 December 2013 |url-status=live |archive-url=https://web.archive.org/web/20131109143313/http://apps.who.int/gb/ebwha/pdf_files/WHA65/A65_20-en.pdf |archive-date=9 November 2013}}</ref>

These efforts have hugely reduced the number of cases; from an estimated 350,000 cases in 1988 to a low of 483 cases in 2001, after which it remained at a level of about 1,000–2000 cases per year for a number of years.<ref name="eradication">{{cite journal |author=Centers for Disease Control Prevention (CDC) |title=Update on vaccine-derived polioviruses |journal=MMWR. Morbidity and Mortality Weekly Report |volume=55 |issue=40 |pages=1093–1097 |date=October 2006 |pmid=17035927}}</ref><ref name="morbidity">{{cite journal |author=Centers for Disease Control and Prevention (CDC) |title=Progress toward interruption of wild poliovirus transmission—worldwide, January 2007 – April 2008 |url=https://www.cdc.gov/mmwr/preview/mmwrhtml/mm5718a4.htm |url-status=live |journal=MMWR. Morbidity and Mortality Weekly Report |volume=57 |issue=18 |pages=489–494 |date=May 2008 |pmid=18463607 |archive-url=https://web.archive.org/web/20170619054233/https://www.cdc.gov/mmwr/preview/mmwrhtml/mm5718a4.htm |archive-date=19 June 2017}}</ref>

By 2015, polio was believed to remain [[Endemic (epidemiology)|naturally spreading]] in only two countries, [[Pakistan]] and [[Afghanistan]],<ref name="eradication1" /><ref name="GlobalPolio2015">{{cite web|title=Wild poliovirus type 1 and Circulating vaccine-derived poliovirus cases|url=http://www.polioeradication.org/dataandmonitoring/poliothisweek.aspx|website=Global Polio Eradication Initiative|access-date=26 December 2015|date=23 December 2015|url-status=live|archive-url=https://web.archive.org/web/20151224045950/http://www.polioeradication.org/Dataandmonitoring/Poliothisweek.aspx|archive-date=24 December 2015}}</ref> although it continued to cause outbreaks in other nearby countries due to hidden or re-established transmission.<ref>Wild Poliovirus case list 2000–2010; data in WHO/HQ as of 9 November 2010 {{cite web |url=http://www.polioeradication.org/tabid/167/iid/80/Default.aspx |title=Emergency appeal for Congo polio outbreak |access-date=17 November 2010 |archive-url=https://web.archive.org/web/20101222075237/http://www.polioeradication.org/tabid/167/iid/80/Default.aspx |archive-date=22 December 2010 }}</ref>

Global surveillance for polio takes two forms. Cases of [[Flaccid paralysis|acute flaccid paralysis]] (AFP) are tested for the presence and type of poliovirus. In addition, environmental and [[Wastewater surveillance|wastewater]] samples are tested for the presence of poliovirus - this is an effective method of detecting circulating virus which has not given rise to severe symptoms.<ref>{{Cite web |date=14 August 2024 |title=Surveillance Indicators |url=https://polioeradication.org/polio-today/polio-now/surveillance-indicators/ |access-date=14 August 2024 |website=Global Polio Eradication Initiative}}</ref> Here is a summary of both wild polio (WPV) and variant polio (cVDPV) prevalence over the years shown:<ref name=":52">{{Cite web |date=9 April 2024 |title=Global Wild Poliovirus 2018–2024 |url=https://polioeradication.org/wp-content/uploads/2024/04/weekly-polio-analyses-WPV-20240409.pdf |website=Global Polio Eradication Initiative - World Health Organization}}</ref><!--update this list annually, delete oldest entry and add new-->

* 2019 - 147 cases of WPV1 in Pakistan, and 29 cases in Afghanistan. None were reported elsewhere in the world. cVDPV was detected in 19 countries with 378 confirmed cases.<ref name=":02">{{Cite journal |last1=Bigouette |first1=John Paul |last2=Wilkinson |first2=Amanda L. |last3=Tallis |first3=Graham |last4=Burns |first4=Cara C. |last5=Wassilak |first5=Steven G. F. |last6=Vertefeuille |first6=John F. |date=2021-08-27 |title=Progress Toward Polio Eradication — Worldwide, January 2019–June 2021 |journal=Morbidity and Mortality Weekly Report |volume=70 |issue=34 |pages=1129–1135 |doi=10.15585/mmwr.mm7034a1 |issn=0149-2195 |pmc=8389387 |pmid=34437527}}</ref>
* 2020 - 84 WPV1 cases in Pakistan, 56 in Afghanistan. 32 countries reported cVDPV detection, and there were 1,103 cVDPV cases.<ref name=":02" />
* In 2021, there were just six confirmed cases of wild poliovirus — one in Pakistan, four in Afghanistan, and one in Malawi. The case in Malawi, the country's first in almost three decades and the first in Africa in five years, was seen as a significant setback to the eradication effort.<ref name="GPEI-Malawi2">{{cite press release |title=GPEI Statement on WPV1 in Malawi: Wild poliovirus type 1 detected in Lilongwe, Malawi |date=2022-02-17 |publisher=Global Polio Eradication Initiative – World Health Organization |url=https://polioeradication.org/news-post/gpei-statement-on-wpv1-in-malawi/}}</ref> 23 countries detected cVDPV, with 698 cases.<ref name=":12">{{cite journal |last=Lee |first=Scarlett E. |date=2023 |title=Progress Toward Poliomyelitis Eradication — Worldwide, January 2021–March 2023 |url=https://www.cdc.gov/mmwr/volumes/72/wr/mm7219a3.htm |journal=MMWR. Morbidity and Mortality Weekly Report |language=en-US |volume=72 |issue=19 |pages=517–522 |doi=10.15585/mmwr.mm7219a3 |issn=0149-2195 |pmc=10208367 |pmid=37167156}}</ref>
* In 2022, there were 30 confirmed cases of WPV1 reported to WHO, with two cases in Pakistan and 20 Afghanistan respectively, while eight non-endemic cases were recorded in Mozambique, the first cases in the country since 1992. The Mozambique cases derived from the strain of Pakistani origin that caused two confirmed cases in Malawi in 2021.<ref>{{cite press release |title=GPEI statement on Mozambique WPV1 detection |date=2022-05-18 |publisher=Global Polio Eradication Initiative – World Health Organization |url=https://polioeradication.org/news-post/gpei-statement-on-mozambique-wpv1-detection/}}</ref> 24 countries detected cVDPV, with 881 cases.<ref name=":12" />
* In 2023, twelve cases of WPV1 were reported, six each in Afghanistan and Pakistan. 32 countries reported cVDPV, with 524 cases.<ref>{{cite journal |last=Geiger |first=Keri |date=2024 |title=Progress Toward Poliomyelitis Eradication — Worldwide, January 2022–December 2023 |url=https://www.cdc.gov/mmwr/volumes/73/wr/mm7319a4.htm |journal=MMWR. Morbidity and Mortality Weekly Report |language=en-US |volume=73 |issue=19 |pages=441–446 |doi=10.15585/mmwr.mm7319a4 |issn=0149-2195 |pmc=11115430 |pmid=38753550}}</ref>

==== Afghanistan and Pakistan ====
{{see also|Polio in Pakistan}}
The last remaining region with wild polio cases are the [[South Asia]]n countries [[Afghanistan]] and [[Pakistan]].<ref name=":5">{{cite web |date=9 April 2024 |title=Global Wild Poliovirus 2018–2024 |url=https://polioeradication.org/wp-content/uploads/2024/04/weekly-polio-analyses-WPV-20240409.pdf |website=Global Polio Eradication Initiative - World Health Organization}}</ref>

During 2011, the [[Central Intelligence Agency|CIA]] ran a fake hepatitis vaccination clinic in [[Abbottabad, Pakistan]], in [[Killing of Osama bin Laden#Intelligence gathering|an attempt to locate]] [[Osama bin Laden]]. This destroyed trust in vaccination programs in the region.<ref>{{Cite journal|vauthors=Kennedy J|date=October 2017|title=How Drone Strikes and a Fake Vaccination Program Have Inhibited Polio Eradication in Pakistan: An Analysis of National Level Data|journal=International Journal of Health Services: Planning, Administration, Evaluation|volume=47|issue=4|pages=807–25|doi=10.1177/0020731417722888|issn=1541-4469|pmid=28764582|s2cid=25844860|url=http://qmro.qmul.ac.uk/xmlui/handle/123456789/25135|access-date=4 May 2021|archive-date=20 October 2021|archive-url=https://web.archive.org/web/20211020082540/https://qmro.qmul.ac.uk/xmlui/handle/123456789/25135|url-status=live}}</ref><ref>{{Cite news|vauthors=McNeil Jr DG|date=9 July 2012|title=C.I.A. Vaccine Ruse May Have Harmed the War on Polio|work=The New York Times|url=https://www.nytimes.com/2012/07/10/health/cia-vaccine-ruse-in-pakistan-may-have-harmed-polio-fight.html|access-date=3 July 2020|issn=0362-4331|archive-date=10 July 2012|archive-url=https://web.archive.org/web/20120710192832/https://www.nytimes.com/2012/07/10/health/cia-vaccine-ruse-in-pakistan-may-have-harmed-polio-fight.html|url-status=live}}</ref> There were attacks and deaths among vaccination workers; 66 vaccinators were killed in 2013 and 2014.<ref>{{cite web|title=Pakistan's fight against polio clashes with battle against Taliban – The National|url=http://www.thenational.ae/world/south-asia/pakistans-fight-against-polio-clashes-with-battle-against-taliban#page2|url-status=live|archive-url=https://web.archive.org/web/20150928122419/http://www.thenational.ae/world/south-asia/pakistans-fight-against-polio-clashes-with-battle-against-taliban#page2|archive-date=28 September 2015|vauthors=Khan T|date=20 January 2015}}</ref><ref name="thenational.ae" /> In Afghanistan, the [[Taliban]] banned house-to-house polio vaccination between 2018 and 2021.<ref>{{cite web |title=House-to-house polio vaccination set to recommence across Afghanistan in November |url=https://www.unicef.org/press-releases/house-house-polio-vaccination-set-recommence-across-afghanistan-november |access-date=2022-06-30 |website=www.unicef.org |archive-date=30 June 2022 |archive-url=https://web.archive.org/web/20220630172858/https://www.unicef.org/press-releases/house-house-polio-vaccination-set-recommence-across-afghanistan-november |url-status=live}}</ref> These factors have set back efforts to eliminate polio by means of vaccination in these countries.<ref>{{cite news |date=20 April 2016 |title=Seven shot dead in Pakistan polio attack |publisher=[[BBC News]] |url=https://www.bbc.com/news/world-asia-36090891 |access-date=25 January 2021 |archive-date=4 October 2019 |archive-url=https://web.archive.org/web/20191004045256/https://www.bbc.com/news/world-asia-36090891 |url-status=live}}</ref>

In Afghanistan, 80 cases of polio were reported from 35 districts during 2011. Incidence over the subsequent 10 years has declined to just 4 cases in 2 districts during 2021.<ref>{{cite web |last=World Health Organization |first=Global Polio Eradication Initiative |date=2022-06-30 |title=Afghanistan Polio Eradication Initiative Annual Report 2021 |url=https://polioeradication.org/wp-content/uploads/2022/06/Afghanistan-Annual-Report-2021.pdf |access-date=30 June 2022 |archive-date=5 June 2022 |archive-url=https://web.archive.org/web/20220605045904/https://polioeradication.org/wp-content/uploads/2022/06/Afghanistan-Annual-Report-2021.pdf |url-status=live}}</ref><ref>{{cite web |title=GPEI-Afghanistan |url=https://polioeradication.org/where-we-work/afghanistan/ |access-date=2022-06-30 |language=en-GB |archive-date=30 June 2022 |archive-url=https://web.archive.org/web/20220630175010/https://polioeradication.org/where-we-work/afghanistan/ |url-status=live}}</ref>

In Pakistan, cases dropped by 97 percent from 2014 to 2018;<ref>{{cite news |title=Nationwide polio campaign starts today |url=https://www.dawn.com/news/1450490 |work=Dawn |date=10 December 2018 |quote=It shows that the number of annual polio cases has decreased by 97 per cent from 306 reported in 2014. |access-date=11 January 2019 |archive-date=6 July 2020 |archive-url=https://web.archive.org/web/20200706000032/https://www.dawn.com/news/1450490 |url-status=live }}</ref> reasons include 440&nbsp;million [[United Arab Emirates dirham|dirham]] support from the [[United Arab Emirates]] to vaccinate more than ten million children,<ref name="thenational.ae">{{cite web|author=The National staff|date=18 April 2015|title=UAE polio campaign vaccinates millions of Pakistani children|url=http://www.thenational.ae/uae/health/uae-polio-campaign-vaccinates-millions-of-pakistani-children|url-status=live|archive-url=https://web.archive.org/web/20150910053250/http://www.thenational.ae/uae/health/uae-polio-campaign-vaccinates-millions-of-pakistani-children|archive-date=10 September 2015}}</ref><ref>{{cite web|url=http://www.thenational.ae/uae/health/17-million-children-to-be-vaccinated-against-polio-in-pakistan|title=17 million children to be vaccinated against polio in Pakistan|author=The National staff|date=24 January 2015|url-status=live|archive-url=https://web.archive.org/web/20150910054826/http://www.thenational.ae/uae/health/17-million-children-to-be-vaccinated-against-polio-in-pakistan|archive-date=10 September 2015}}</ref> changes in the military situation, and arrests of some of those who attacked polio workers.<ref name=BBC2016>{{cite news|url=https://www.bbc.co.uk/news/world-asia-36300034|title=Pakistan could beat polio in months, says WHO|date=16 May 2016|publisher=BBC News|access-date=16 May 2016|url-status=live|archive-url=https://web.archive.org/web/20160516114003/http://www.bbc.co.uk/news/world-asia-36300034|archive-date=16 May 2016}}</ref><ref>{{cite news|url=https://www.bbc.com/news/world-asia-32996624|title=Polio in Pakistan: Drop of 70% recorded this year|publisher=BBC News|url-status=live|archive-url=https://web.archive.org/web/20150604035928/http://www.bbc.com/news/world-asia-32996624|archive-date=4 June 2015|date=3 June 2015}}</ref>

==== Americas ====
The [[Americas]] were declared polio-free in 1994.<ref name=MMWR_1994>{{cite journal | title = Certification of poliomyelitis eradication—the Americas, 1994 | journal = MMWR. Morbidity and Mortality Weekly Report | volume = 43 | issue = 39 | pages = 720–2 | date = October 1994 | pmid = 7522302 | url = https://www.cdc.gov/mmwr/preview/mmwrhtml/00032760.htm | url-status = live | archive-url = https://web.archive.org/web/20170521163051/https://www.cdc.gov/mmwr/preview/mmwrhtml/00032760.htm | archive-date = 21 May 2017 | author1 = Centers for Disease Control Prevention (CDC) }}</ref> The last known case was a boy in [[Peru]] in 1991.<ref>{{Cite web|url=https://www.historyofvaccines.org/content/polio-declared-eliminated-americas|title=Polio Declared Eliminated from the Americas &#124; History of Vaccines|access-date=23 May 2020|archive-date=9 July 2020|archive-url=https://web.archive.org/web/20200709100144/https://www.historyofvaccines.org/content/polio-declared-eliminated-americas}}</ref> The US [[Centers for Disease Control and Prevention]] recommends polio vaccination boosters for travelers and those who live in countries where the disease is endemic.<ref>{{cite web |date=2 June 2014 |title=Guidance to US Clinicians Regarding New WHO Polio Vaccination Requirements for Travel by Residents of and Long-term Visitors to Countries with Active Polio Transmission |url=http://emergency.cdc.gov/han/han00362.asp |archive-url=https://web.archive.org/web/20140604000158/http://emergency.cdc.gov/han/han00362.asp |archive-date=4 June 2014 |access-date=4 June 2014 |website=CDC}}</ref>

In July 2022, the US state of [[New York (state)|New York]] reported a polio case for the first time in almost a decade in the country; this was attributed to a vaccine-derived strain of the virus.<ref>{{cite web |last=Kimball |first=Spencer |title=How polio came back to New York for the first time in decades, silently spread and left a patient paralyzed |url=https://www.cnbc.com/2022/10/04/how-polio-silently-spread-in-new-york-and-left-a-person-paralyzed.html |access-date=2022-11-15 |publisher=CNBC |date=4 October 2022 |archive-date=15 November 2022 |archive-url=https://web.archive.org/web/20221115092909/https://www.cnbc.com/2022/10/04/how-polio-silently-spread-in-new-york-and-left-a-person-paralyzed.html |url-status=live}}</ref>

==== Western Pacific ====
In 2000, polio was declared to have been officially eliminated in 37 Western Pacific countries, including China and Australia.<ref name=Pacific>{{cite journal | title = General News. Major Milestone reached in Global Polio Eradication: Western Pacific Region is certified Polio-Free | journal = Health Education Research | year = 2001 | volume = 16 | issue = 1 | pages = 109–114 | doi = 10.1093/her/16.1.109 | bibcode = 2001PDiff..16..110Y | last1 = Yamazaki | first1 = S. | last2 = Toraya | first2 = H. }}</ref><ref name="D'Souza_2002">{{cite journal | vauthors = D' Souza RM, Kennett M, Watson C | title = Australia declared polio free | journal = Communicable Diseases Intelligence Quarterly Report | volume = 26 | issue = 2 | pages = 253–60 | year = 2002 | pmid = 12206379 }}</ref>

Despite eradication ten years earlier, an outbreak was confirmed in China in September 2011, involving a strain common in Pakistan.<ref>{{cite news | url=http://www.cnn.com/2011/09/21/health/china-polio-outbreak/index.html | work=CNN | title=New polio outbreak hits China - CNN.com | date=21 September 2011 | url-status=live | archive-url=https://web.archive.org/web/20120101174601/http://www.cnn.com/2011/09/21/health/china-polio-outbreak/index.html | archive-date=1 January 2012 }}</ref>

In September 2019, the [[Department of Health (Philippines)|Department of Health of the Philippines]] declared a polio outbreak in the country after a single case in a 3-year-old girl.<ref name="Polio in PH">{{Cite news |vauthors=Paris J |url=https://www.rappler.com/nation/240493-polio-back-philippines |title=PH declares polio outbreak as disease returns after 19 years |work=[[Rappler]] |location=Manila, Philippines |date=19 September 2019 |access-date=22 September 2019 |archive-date=22 September 2019 |archive-url=https://web.archive.org/web/20190922014536/https://www.rappler.com/nation/240493-polio-back-philippines |url-status=live }}</ref> In December 2019, acute poliomyelitis was confirmed in an infant in [[Sabah|Sabah state]], [[Borneo]], [[Malaysia]].<ref name="VOAMalaysia">{{cite news |date=9 December 2019 |title=Malaysia Reports First Case of Polio in 27 Years |work=[[VOA News]] |agency=[[Associated Press]] |url=https://www.voanews.com/a/science-health_malaysia-reports-first-case-polio-27-years/6180817.html |access-date=10 December 2019 |archive-date=8 January 2020 |archive-url=https://web.archive.org/web/20200108134117/https://www.voanews.com/science-health/malaysia-reports-first-case-polio-27-years |url-status=live }}</ref> Subsequently, a further three polio cases were reported, with the last case reported in January 2020. Both outbreaks were found to be linked instances of vaccine-derived poliomyelitis.<ref>{{Cite journal |last1=Snider |first1=Cynthia J. |last2=Boualam |first2=Liliane |last3=Tallis |first3=Graham |last4=Takashima |first4=Yoshihiro |last5=Abeyasinghe |first5=Rabindra |last6=Lo |first6=Ying-Ru |last7=Grabovac |first7=Varja |last8=Avagyan |first8=Tigran |last9=Aslam |first9=Syeda Kanwal |last10=Eltayeb |first10=Abu Obeida |last11=Aung |first11=Khin Devi |last12=Wang |first12=Xiaojun |last13=Shrestha |first13=Achyut |last14=Ante-Orozco |first14=Carla |last15=Silva |first15=Maria Wilda T. |date=2022-03-23 |title=Concurrent outbreaks of circulating vaccine-derived poliovirus types 1 and 2 affecting the Republic of the Philippines and Malaysia, 2019–2021 |journal=Vaccine |volume=41 |issue=Suppl 1 |pages=A58–A69 |doi=10.1016/j.vaccine.2022.02.022 |pmid=35337673 |pmc=10546869 |s2cid=247652342 |issn=0264-410X |doi-access=free}}</ref>

==== Europe ====
[[Europe]] was declared polio-free in 2002.<ref name=WHO_Europe_2002>{{cite press release |title=Europe achieves historic milestone as Region is declared polio-free |publisher=European Region of the World Health Organization |date=21 June 2002 |url=https://www.who.int/mediacentre/news/releases/releaseeuro02/en/index.html |access-date=23 August 2008 |archive-url=https://web.archive.org/web/20080916065107/http://www.who.int/mediacentre/news/releases/releaseeuro02/en/index.html |archive-date=16 September 2008}}</ref>

==== Southeast Asia ====
On 27 March 2014, the WHO announced the eradication of poliomyelitis in the South-East Asia Region, which includes eleven countries: [[Bangladesh]], [[Bhutan]], [[North Korea]], [[India]], [[Indonesia]], [[Maldives]], [[Myanmar]], [[Nepal]], [[Sri Lanka]], [[Thailand]] and [[Timor-Leste]].<ref name="eradication1">{{cite web |url=http://www.searo.who.int/mediacentre/releases/2014/pr1569/en/ |title=WHO South-East Asia Region certified polio-free |publisher=WHO |date=27 March 2014 |access-date=27 March 2014 |archive-url=https://web.archive.org/web/20140327235218/http://www.searo.who.int/mediacentre/releases/2014/pr1569/en/ |archive-date=27 March 2014}}</ref> With the addition of this region, 80 per cent of the world population was considered to be living in polio-free regions.<ref name="eradication1"/>

==== Middle East ====
{{As of|2023|January}}, [[Syria]] is considered a polio-free country, but it remains at high risk for imported outbreaks.<ref name=":8">{{Cite web |date=26 January 2023 |title=Syria takes steps to advance polio transition while strengthening essential health priorities |url=https://www.who.int/news-room/feature-stories/detail/syria-takes-steps-to-advance-polio-transition-while-strengthening-essential-health-priorities |access-date=2025-06-20 |website=World Health Organization |language=en}}</ref> Difficulties in executing immunization programs in the ongoing [[Syrian Civil War|civil war]] led to a return of wild polio in 2012–2013<ref name=":8" /> 15 cases were confirmed among children in [[Syria]] between October and November 2013 in [[Deir Ezzor]]. Later, two more cases, one each in rural [[Damascus]] and [[Aleppo]], were identified.<ref>{{cite news |date=26 November 2013 |title=Syria polio cases spread to Damascus and Aleppo – WHO |url=http://www.dnaindia.com/health/report-syria-polio-cases-spread-to-damascus-and-aleppo-who-1925221 |url-status=live |archive-url=https://web.archive.org/web/20131128140419/http://www.dnaindia.com/health/report-syria-polio-cases-spread-to-damascus-and-aleppo-who-1925221 |archive-date=28 November 2013 |access-date=26 November 2013 |work=DNA}}</ref> A vaccination campaign in Syria operated under gunfire and led to the deaths of several vaccinators,<ref>{{cite web |last=Motlagh |first=Jason |title=Fighting Polio Amid the Chaos of Syria's Civil War |url=http://news.nationalgeographic.com/2015/03/150305-polio-syria-iraq-islamic-state-refugees-vaccination-virus-jihad/ |work=National Geographic |date=5 March 2015 |archive-url=https://web.archive.org/web/20160105100254/http://news.nationalgeographic.com/2015/03/150305-polio-syria-iraq-islamic-state-refugees-vaccination-virus-jihad/ |archive-date=5 January 2016}}</ref> but returned vaccination coverage to pre-war levels.<ref>{{cite news |vauthors=Westall S |title=Polio immunisation rate in Syria close to pre-war level – WHO |url=https://www.reuters.com/article/mideast-crisis-syria-polio-idUSL6N0V70ZW20150128 |url-status=live |publisher=[[Reuters]] |date=28 January 2015 |archive-url=https://web.archive.org/web/20150924212925/http://www.reuters.com/article/2015/01/28/mideast-crisis-syria-polio-idUSL6N0V70ZW20150128 |archive-date=24 September 2015}}</ref> Another outbreak in 2017 was caused by circulating vaccine-derived poliovirus type 2 (cVDPV2). Both outbreaks were successfully contained through intensive vaccination campaigns and surveillance efforts.<ref name=":8" /> 

In 2022, prior to the [[Gaza–Israel conflict|Israel-Hamas conflict]], routine immunization coverage of eligible children exceeded 99%, but fell to less than 90% by the first quarter of 2024, according to the [[World Health Organization|WHO]].<ref>{{cite web |title=Humanitarian pauses vital for critical polio vaccination campaign in the Gaza Strip |url=https://www.who.int/news/item/16-08-2024-humanitarian-pauses-vital-for-critical-polio-vaccination-campaign-in-the-gaza-strip |access-date=2024-12-14 |website=www.who.int}}</ref> In 2024, the [[Gaza Health Ministry]] reported that several children have shown symptoms consistent with polio, with laboratory tests confirming that a 10-month-old child is infected with the virus.<ref>{{cite news |last=Pietsch |first=Bryan |date=2024-08-17 |title=Gaza faces public health crisis with first confirmed case of polio |url=https://www.washingtonpost.com/world/2024/08/17/gaza-strip-polio-case-confirmed/ |access-date=2024-08-18 |newspaper=[[The Washington Post]] |language=en-US |issn=0190-8286}}</ref> [[United Nations]] Secretary-General [[António Guterres]] urged for a weeklong cease-fire in Gaza to facilitate vaccinations and prevent a potential polio outbreak, emphasizing the risk faced by many children.<ref>{{cite news |last1=Fassihi |first1=Farnaz |last2=Livni |first2=Ephrat |date=2024-08-16 |title=The U.N. Calls for a Temporary Truce to Fight Polio in Gaza |url=https://www.nytimes.com/2024/08/16/world/middleeast/gaza-polio-crisis.html |access-date=2024-08-18 |work=The New York Times |language=en-US |issn=0362-4331}}</ref>

==== Africa ====
[[File:Polio Vaccination - Egypt (16868521330).jpg|thumb|Polio vaccination in Egypt]]
In 2003, in [[Northern Region, Nigeria|northern Nigeria]]&nbsp;– a country that at that time was considered provisionally polio free&nbsp;– a [[fatwa]] was issued declaring that the polio vaccine was designed to render children sterile.<ref>{{cite web |url=http://www.unicef.org/cbsc/index_49534.html |title=Polio Eradication Efforts in Nigeria and India |access-date=25 December 2013 |website=UNICEF |url-status=live |archive-url=https://web.archive.org/web/20131225195534/http://www.unicef.org/cbsc/index_49534.html |archive-date=25 December 2013}}</ref> Subsequently, polio reappeared in Nigeria and spread from there to several other countries. In 2013, nine health workers administering polio vaccine were targeted and killed by gunmen on motorcycles in [[Kano (city)|Kano]], but this was the only attack.<ref>{{cite news |url=https://www.bbc.co.uk/news/world-africa-21381773 |title=Nigeria polio vaccinators shot dead in Kano |publisher=BBC News |url-status=live |archive-url=https://web.archive.org/web/20141228034024/http://www.bbc.co.uk/news/world-africa-21381773 |archive-date=28 December 2014 |date=8 February 2013}}</ref><ref>{{cite news |url=https://www.bbc.co.uk/news/world-africa-33650543 |publisher=BBC News |title=Nigeria marks one year without recorded polio case |date=24 July 2015 |url-status=live |archive-url=https://web.archive.org/web/20150724162448/http://www.bbc.co.uk/news/world-africa-33650543 |archive-date=24 July 2015}}</ref> Local traditional and religious leaders and polio survivors worked to revive the campaign,<ref name="reuters.com">{{cite news |url=https://www.reuters.com/article/us-health-polio-nigeria-idUSKCN0PX2RF20150723 |publisher=Reuters |title=Nigeria marks polio-free year, raising global eradication hopes |date=23 July 2015 |url-status=live |archive-url=https://web.archive.org/web/20151119091530/http://www.reuters.com/article/2015/07/23/us-health-polio-nigeria-idUSKCN0PX2RF20150723 |archive-date=19 November 2015}}</ref> and Nigeria was removed from the polio-endemic list in September 2015 after more than a year without any cases,<ref>{{cite news |url=https://www.who.int/mediacentre/news/releases/2015/nigeria-polio/en/ |publisher=[[WHO]] |title=WHO Removes Nigeria from Polio-Endemic List |date=26 September 2015 |access-date=8 January 2016 |archive-url=https://web.archive.org/web/20160119165136/http://www.who.int/mediacentre/news/releases/2015/nigeria-polio/en/ | archive-date=19 January 2016 }}</ref> only to be restored to the list in 2016 when two cases were detected.<ref name=Nigeria2016>{{cite web|title=Government of Nigeria reports 2 wild polio cases, first since July 2014|url=https://www.who.int/mediacentre/news/releases/2016/nigeria-polio/en/|website=WHO|access-date=15 August 2016|date=11 August 2016|url-status=live|archive-url=https://web.archive.org/web/20160815045938/http://www.who.int/mediacentre/news/releases/2016/nigeria-polio/en/|archive-date=15 August 2016}}</ref>

Africa was declared free of wild polio in August 2020, although cases of circulating vaccine-derived poliovirus type 2 continue to appear in several countries.<ref>{{cite journal |last=Guglielmi |first=Giorgia |date=2020-08-28 |title=Africa declared free from wild polio — but vaccine-derived strains remain |url=https://www.nature.com/articles/d41586-020-02501-3 |journal=Nature |doi=10.1038/d41586-020-02501-3 |pmid=32860027 |s2cid=221365928 |access-date=1 July 2022 |archive-date=1 July 2022 |archive-url=https://web.archive.org/web/20220701110900/https://www.nature.com/articles/d41586-020-02501-3 |url-status=live|url-access=subscription }}</ref>

A single case of wild polio that was detected in [[Malawi]] in February 2022, and another in [[Mozambique]] in May 2022 were both of a strain imported from Pakistan and do not affect the African region's wild poliovirus-free certification status.<ref>{{cite web |title=Malawi declares polio outbreak |url=https://www.afro.who.int/news/malawi-declares-polio-outbreak |access-date=2022-06-29 |website=WHO {{!}} Regional Office for Africa |archive-date=16 June 2022 |archive-url=https://web.archive.org/web/20220616195336/https://www.afro.who.int/news/malawi-declares-polio-outbreak |url-status=live}}</ref><ref>{{cite web |date=2022-05-18 |title=First polio outbreak in 30 years declared in Mozambique |url=https://news.un.org/en/story/2022/05/1118502 |access-date=2022-07-01 |website=UN News |archive-date=1 July 2022 |archive-url=https://web.archive.org/web/20220701110841/https://news.un.org/en/story/2022/05/1118502 |url-status=live}}</ref>

== History ==
{{see also|History of poliomyelitis|List of poliomyelitis survivors}}
[[File:Polio Egyptian Stele.jpg|thumb|left|An [[Ancient Egypt|Egypt]]ian [[stele]] thought to represent a person with polio, [[18th Dynasty]] (1403–1365 BC)]]
The effects of polio have been known since [[prehistory]]; [[Ancient Egypt|Egyptian]] paintings and carvings depict otherwise healthy people with withered limbs, and young children walking with canes.<ref name=Paul_1971>{{cite book| author = Paul JR| title=A History of Poliomyelitis| publisher=Yale University Press| location= New Haven, Conn| year=1971| pages=16–18| isbn= 978-0-300-01324-5| series= Yale studies in the history of science and medicine}}</ref> The earliest known case of polio is indicated by the remains of a teenage girl discovered in a 4000-year-old burial site in the [[History of the United Arab Emirates|United Arab Emirates]], exhibiting characteristic symptoms of the condition.<ref>{{Cite book |last1=Renfrew |first1=Colin |title=Archaeology: Theories, Methods, and Practice |last2=Bahn |first2=Paul |publisher=Thames & Hudson |year=2012 |isbn=978-0-500-28976-1 |edition=6th |page=447}}</ref>

The first clinical description was provided by the English physician [[Michael Underwood (physician)|Michael Underwood]] in 1789, where he refers to polio as "a debility of the lower extremities".<ref name="Underwood_1789">{{cite book | author = Underwood M | author-link = Michael Underwood (physician) | chapter = Debility of the lower extremities|title=A treatise on the diseases of children, with general directions for the management of infants from the birth (1789) | volume = 2 | publisher = J. Mathews | location=London | year = 1789 | pages = 88–91 | chapter-url=https://archive.org/stream/b21516728_0002#page/n103/mode/2up}}</ref> The work of physicians [[Jakob Heine]] in 1840 and [[Karl Oskar Medin]] in 1890 led to it being known as ''Heine–Medin disease''.<ref name="Pearce_2005">{{cite journal | vauthors = Pearce JM | title = Poliomyelitis (Heine–Medin disease) | journal = Journal of Neurology, Neurosurgery, and Psychiatry | volume = 76 | issue = 1 | page = 128 | date = January 2005 | pmid = 15608013 | pmc = 1739337 | doi = 10.1136/jnnp.2003.028548 }}</ref> The disease was later called ''infantile paralysis'', based on its propensity to affect children.<ref>{{cite book |author=Gould T |url=https://archive.org/details/summerplaguepoli0000goul |title=A Summer Plague: Polio and its Survivors |publisher=Yale University Press |year=1995 |isbn=0-300-06292-3 |chapter=Chapter One}}</ref>

Before the 20th century, polio infections were rarely seen in infants before six months of age, most cases occurring in children six months to four years of age. Poorer [[sanitation]] of the time resulted in constant exposure to the virus, which enhanced a natural [[immunity (medical)|immunity]] within the population. In developed countries during the late 19th and early 20th centuries, improvements were made in community sanitation, including better [[sewage]] disposal and clean water supplies. These changes drastically increased the proportion of children and adults at risk of paralytic polio infection, by reducing childhood exposure and immunity to the disease.<ref name="Robertson_1993">{{cite web | author = Robertson S | title = Module 6: Poliomyelitis | work = The Immunological Basis for Immunization Series | publisher = World Health Organization. Geneva, Switzerland. | url = http://whqlibdoc.who.int/hq/1993/WHO_EPI_GEN_93.16_mod6.pdf?ua=1 | format = PDF | year = 1993 | access-date = 23 August 2008 | archive-url = https://web.archive.org/web/20140202115733/http://whqlibdoc.who.int/hq/1993/WHO_EPI_GEN_93.16_mod6.pdf?ua=1 | archive-date = 2 February 2014 }}</ref>

Small localized paralytic polio [[epidemic]]s began to appear in Europe and the United States around 1900.<ref name = Trevelyan>{{cite journal | vauthors = Trevelyan B, Smallman-Raynor M, Cliff AD | title = The Spatial Dynamics of Poliomyelitis in the United States: From Epidemic Emergence to Vaccine-Induced Retreat, 1910–1971 | journal = Annals of the Association of American Geographers| volume = 95 | issue = 2 | pages = 269–93 | date = June 2005 | pmid = 16741562 | pmc = 1473032 | doi = 10.1111/j.1467-8306.2005.00460.x | bibcode = 2005AAAG...95..269T }}</ref> Outbreaks reached [[pandemic]] proportions in Europe, North America, Australia, and New Zealand during the first half of the 20th century. By 1950, the peak age incidence of paralytic poliomyelitis in the United States had shifted from infants to children aged five to nine years, when the risk of paralysis is greater; about one-third of the cases were reported in persons over 15 years of age.<ref name=Melnick_1990>{{cite book | author = Melnick JL | title = Poliomyelitis. In: Tropical and Geographical Medicine | edition = 2nd | publisher = McGraw-Hill | year =1990 | pages = 558–76 | isbn = 978-0-07-068328-0 }}</ref> Accordingly, the rate of paralysis and death due to polio infection also increased during this time.<ref name = Trevelyan/> In the United States, the 1952 polio epidemic became the worst outbreak in the nation's history.  Of the nearly 58,000 cases reported that year, 3,145 died and 21,269 were left with mild to disabling paralysis.<ref name="Zamula">{{cite journal |author = Zamula E |title = A New Challenge for Former Polio Patients |url = https://www.questia.com/library/1G1-10942759/a-new-challenge-for-former-polio-patients |journal = FDA Consumer |volume = 25 |issue = 5 |pages = 21–25 |year = 1991 |archive-url = https://web.archive.org/web/20140220034400/http://www.questia.com/library/1G1-10942759/a-new-challenge-for-former-polio-patients |archive-date = 20 February 2014 }}<!-- url returns NET::ERR_CERT_DATE_INVALID error --></ref> [[Intensive care medicine]] has its origin in the fight against polio.<ref>{{cite web|url=https://docs.google.com/viewer?a=v&pid=explorer&chrome=true&srcid=0B7CdB217pf6yN2QxOGI5NTUtZWIzYS00N2NhLWFhODQtOGZjMjdhZTlkZGE5 |title= Louise Reisner-Sénélar (2009) The Danish anaesthesiologist Björn Ibsen a pioneer of long-term ventilation on the upper airways}}</ref> Most hospitals in the 1950s had limited access to [[iron lung]]s for patients unable to breathe without mechanical assistance. Respiratory centers designed to assist the most severe polio patients, first established in 1952 at the Blegdam Hospital of [[Copenhagen]] by [[Denmark|Danish]] [[anesthesia|anesthesiologist]] [[Bjørn Aage Ibsen|Bjørn Ibsen]], were the precursors of modern [[intensive care unit]]s (ICU). (A year later, Ibsen would establish the world's first dedicated ICU.)<ref>{{cite journal| vauthors = Pincock S |title=Bjørn Aage Ibsen|journal=The Lancet|editor=Elsevier|year=2007|volume=370|issue=9598|page=1538|doi=10.1016/S0140-6736(07)61650-X|s2cid=54311450|doi-access=free}}</ref>

The polio epidemics not only altered the lives of those who survived them, but also brought profound cultural changes, spurring [[grassroots]] fund-raising campaigns that would revolutionize medical [[philanthropy]], and giving rise to the modern field of [[Physical therapy|rehabilitation therapy]]. As one of the largest disabled groups in the world, polio survivors also helped to advance the modern [[disability rights movement]] through campaigns for the social and civil rights of the [[disabled]]. The World Health Organization estimates that there are 10 to 20&nbsp;million polio survivors worldwide.<ref name=NewsDesk>{{cite web | title = After Effects of Polio Can Harm Survivors 40 Years Later | publisher = March of Dimes | url = http://www.marchofdimes.org/news/after-effects-of-polio-can-harm-survivors-40-years-later.aspx | date = 1 June 2001 | access-date = 14 November 2014 | url-status = live | archive-url = https://web.archive.org/web/20141225210413/http://www.marchofdimes.org/news/after-effects-of-polio-can-harm-survivors-40-years-later.aspx | archive-date = 25 December 2014 }}</ref> In 1977, there were 254,000 persons living in the United States who had been paralyzed by polio.<ref>{{cite journal | vauthors = Frick NM, Bruno RL | title = Post-polio sequelae: physiological and psychological overview | journal = Rehabilitation Literature | volume = 47 | issue = 5–6 | pages = 106–11 | year = 1986 | pmid = 3749588 }}</ref> According to doctors and local polio support groups, some 40,000 polio survivors with varying degrees of paralysis were living in Germany, 30,000 in Japan, 24,000 in France, 16,000 in Australia, 12,000 in Canada and 12,000 in the United Kingdom in 2001.<ref name= NewsDesk/> Many [[List of polio survivors|notable individuals have survived polio]] and often credit the prolonged immobility and residual paralysis associated with polio as a driving force in their lives and careers.<ref>{{cite book | vauthors = Bruno RL |title=The Polio Paradox: Understanding and Treating "Post-Polio Syndrome" and Chronic Fatigue |publisher=Warner Books |location=New York |year=2002 |pages= 105–06|isbn=978-0-446-69069-0 }}</ref>

The disease was very well publicized during the polio epidemics of the 1950s, with extensive media coverage of any scientific advancements that might lead to a cure. Thus, the scientists working on polio became some of the most famous of the century. Fifteen scientists and two laymen who made important contributions to the knowledge and treatment of poliomyelitis are honored by the [[Polio Hall of Fame]], which was dedicated in 1957 at the [[Roosevelt Warm Springs Institute for Rehabilitation]] in [[Warm Springs, Georgia|Warm Springs]], Georgia, US. In 2008 four organizations (Rotary International, the World Health Organization, the U.S. Centers for Disease Control and UNICEF) were added to the Hall of Fame.<ref>{{cite news | vauthors = Skinner W | title=Four added to Polio Hall of Fame at Warm Springs | date=15 November 2008 | url=http://www.times-herald.com/Local/Four-added-to-Polio-Hall-of-Fame-at-Warm-Springs-589785 | work=The Times-Herald (Newnan, GA) | access-date=29 May 2009 | archive-url=https://web.archive.org/web/20100328073707/http://www.times-herald.com/Local/Four-added-to-Polio-Hall-of-Fame-at-Warm-Springs-589785 | archive-date=28 March 2010 }}</ref><ref>{{cite news | title=CDC Inducted into Polio Hall of Fame | date=23 January 2009 | url =https://www.cdc.gov/news/2009/01/polio_hof/ | work =CDC in the News |archive-url=https://web.archive.org/web/20150924132112/https://www.cdc.gov/news/2009/01/polio_hof/|archive-date=24 September 2015}}</ref>

[[World Polio Day]] (24 October) as an annual day of awareness was established by [[Rotary International]] to commemorate the birth of [[Jonas Salk]], who led the first team to develop a vaccine against poliomyelitis.<ref name=":3">{{cite web |date=19 October 2012 |title=Announcement: World Polio Day – 24 October 2012 |url=https://www.cdc.gov/mmwr/preview/mmwrhtml/mm6141a6.htm |url-status=live |archive-url=https://web.archive.org/web/20131212113105/http://www.cdc.gov/mmwr/preview/mmwrhtml/mm6141a6.htm |archive-date=12 December 2013 |access-date=7 December 2013 |website=CDC |publisher=Centers for Disease Control and Prevention}}</ref>

A global effort to [[Eradication of infectious disease|eradicate]] polio – the [[Global Polio Eradication Initiative]] (GPEI) – began in 1988, led by the [[World Health Organization]], [[UNICEF]], and [[The Rotary Foundation]].<ref name=":1" /> Since then, international cooperation led by GPEI has reduced polio worldwide by 99 percent, and the campaign is ongoing.<ref name=":3" />

In 2010, wild poliovirus was discovered through importation in 13 different countries. They were [[Chad]], the [[DRC|Democratic Republic of Congo]], the [[RO Congo|Republic of Congo]], [[Kazakhstan]], [[Liberia]], [[Mali]], [[Nepal]], [[Niger]], the [[Russian Federation]], [[Senegal]], [[Tajikistan]], [[Turkmenistan]], and [[Uganda]].<ref>{{cite web |date=2010 |title=Every Last Child, Annual Report 2010 |url=https://polioeradication.org/wp-content/uploads/2016/07/GPEI_AR2010_EN.pdf |access-date=3 June 2024 |website=polioeradication.org |page=13}}</ref>

[[File:A displaced child receives a polio vaccination in UNRWA shelter in Beach camp , Gaza Strip.jpg|thumb|Polio vaccines being administered in [[Al-Shati refugee camp]] during the [[2024 Gaza Strip polio epidemic|2024&ndash;25 Gaza Strip polio epidemic]]]]
In 2021, Types 2 and 3 were fully eradicated from every country; however, type 1 cases still remain in Pakistan and Afghanistan.<ref name=":6">{{cite web |title=Poliomyelitis (polio) |url=https://www.who.int/health-topics/poliomyelitis |access-date=2024-06-04 |website=www.who.int}}</ref> A majority of countries have successfully eradicated polio, with Pakistan and Afghanistan being the last countries with endemic cases of poliovirus.<ref name=":7">{{cite web |title=Progress towards polio eradication |url=https://ourworldindata.org/grapher/progress-towards-polio-eradication |access-date=2024-06-04 |website=Our World in Data}}</ref> The following countries have been considered polio-free, but not confirmed as of April 2024: Somalia, Djibouti, Sudan, Egypt, Libya, Tunisia, Morocco, Palestine, Lebanon, Syria, Jordan, Saudi Arabia, Bahrain, Qatar, Oman, Yemen, the UAE, Iraq, Kuwait, and Iran.<ref name=":7" />

==Research==
Since 2018, [[Global Polio Eradication Initiative]] (GPEI) has coordinated efforts both to eliminate polio and to research means of improving surveillance and prevention. At the peak of its work, the programme directly employed 4000 people across 75 countries and managed a budget of nearly U.S. $1&nbsp;billion.<ref name="Aylward2011">{{cite book |last=Aylward |first=Bruce |url=https://books.google.com/books?id=Q9bxCwAAQBAJ |title=Disease Eradication in the 21st Century: Implications for Global Health |publisher=The MIT Press |year=2011 |isbn=978-0-262-01673-5 |editor=Cochi |editor-first=Stephen L. |location=Cambridge |pages=13–24 |chapter=2. Lessons from the late stages of the global polio eradication initiative |editor-last2=Dowdle |editor-first2=Walter R.}}</ref>

{{as of|2021}}, the GPEI had raised 18&nbsp;billion dollars in funding,<ref name="finance">{{Cite web |title=GPEI-Historical Contributions, 1988-2020 |url=https://polioeradication.org/financing/donors/historical-contributions/}}</ref> with annual contributions around 800 million to 1&nbsp;billion dollars. Around 30% of the funding came from the [[Gates Foundation]] 30% from developed governments, 27% from countries at risk of polio, and the rest was made up of donations from nonprofits, private funders, and other foundations.<ref>{{cite web |title=Vaccination funding landscape |url=http://www.givewell.org/international/charities/vaccination-organizations#Eradicationinitiatives |access-date=20 June 2016 |website=Givewell.org}}</ref>

The GPEI has identified six directions for continuing research:<ref>{{cite web |title=GPEI-Research + Innovation |url=https://polioeradication.org/tools-and-library/current-research-areas/ |access-date=2024-04-17 |website=Global Polio Eradication Initiative - World Health Organization |language=en-GB}}</ref>

* Optimizing oral polio vaccine efficacy
* Developing affordable inactivated polio vaccine
* Managing risks associated with vaccine-derived polioviruses and vaccine-associated paralytic polio (including OPV cessation)
* Antivirals
* Polio diagnostics
* Surveillance research

Even if polio can be eliminated from the world population, vaccination programs should continue for at least ten years.<ref name=":4">{{cite journal |last1=Lopez Cavestany |first1=Rocio |last2=Eisenhawer |first2=Martin |last3=Diop |first3=Ousmane M. |last4=Verma |first4=Harish |last5=Quddus |first5=Arshad |last6=Mach |first6=Ondrej |title=The Last Mile in Polio Eradication: Program Challenges and Perseverance |journal=Pathogens |volume=13 |issue=4 |pages=323 |date=April 2024 |issn=2076-0817 |pmid=38668278 |pmc=11053864 |doi=10.3390/pathogens13040323 |doi-access=free}}</ref> The retention of live poliovirus samples in laboratories and vaccine manufacturing facilities (which carry a risk of escape of the virus) should progressively be reduced. To support these two objectives, vaccines are under development which either utilise a [[virus-like particle]], or which derive from a modified virus which cannot reproduce in a human host.<ref name=":4" />

== References ==
{{reflist}}

== Further reading ==
{{external media| float = right| video1 = [https://www.c-span.org/video/?193162-1/polio-american-story Presentation by David Oshinsky on ''Polio'', June 21, 2006], [[C-SPAN]]| video2 = [https://www.c-span.org/video/?195258-2/polio-american-story Presentation by Oshinsky on ''Polio'', October 8, 2006], [[C-SPAN]]}}

* Benison, Saul. “The Enigma of Poliomyelitis: 1910,” in ''Freedom and Reform: Essays in Honor of Henry Steele Commager,'' ed. Harold Hyman, (1967).
* Benison, Saul.  “The History of Polio Research in the United States: Appraisal and Lessons,” in ''The Twentieth Century Sciences: Studies in the Biography of Ideas,'' ed. Gerald Holton, (1972).

* Black, Kathryn. ''In the shadow of polio : a personal and social history'' (1996) [https://archive.org/details/inshadowofpoliop00blac online]

* {{cite book|author = Gould, Tony|title=A Summer Plague: Polio and Its Survivors |url=https://yalebooks.co.uk/book/9780300072761/a-summer-plague/|publisher=Yale University Press|location=London|year=1995}}

* Hecht, Alan, and I. Edward Alcamo. ''Polio'' (2003) [https://archive.org/details/poliodeadlydisea00alan/page/n7/mode/2up online copy], for middle schools

* {{cite book|author = Kluger Jefferey|title=Splendid Solution: Jonas Salk and the Conquest of Polio |url= https://books.google.com/books?id=PE6rXNMlwmkC&q=Splendid+Solution+-+Jonas+Salk+and+the+Conquest+of+Polio |publisher=G. P. Putnam's Sons|location=New York |year=2004 |isbn=978-0-399-15216-0 }}
* {{cite book | vauthors = Oshinsky DM |title=Polio: An American story |publisher=Oxford University Press |location=Oxford |year=2005 |isbn=978-0-19-515294-4 |url= https://archive.org/details/polioamericansto00oshi |url-access=registration}}, a major scholarly history.

* Rai, Anushree, et al. "Polio returns to the USA: An epidemiological alert." ''Annals of Medicine and Surgery'' 82 (2022). [https://www.sciencedirect.com/science/article/pii/S2049080122013231 online]

* {{cite book | vauthors = Shaffer MM, Bernard S |title=The death of a disease: a history of the eradication of poliomyelitis |publisher=Rutgers University Press |location=New Brunswick, NJ |year=2005 |isbn=978-0-8135-3677-4 |url= https://books.google.com/books?id=iKidtL80imMC&q=polio }}
* {{cite book | vauthors = Shell M |title=Polio and its aftermath: the paralysis of culture |publisher=Harvard University Press |location=Cambridge |year=2005 |isbn=978-0-674-01315-5 |url= https://archive.org/details/polioitsaftermat00shel |url-access=registration |quote=polio. }}
* {{cite book | vauthors = Wilson DJ |title=Living with polio: the epidemic and its survivors |publisher=University of Chicago Press |location=Chicago |year=2005 |isbn=978-0-226-90103-9 |url= https://books.google.com/books?id=Ejvjfo_K-IQC&q=polio }}
* {{cite book | vauthors = Wilson DJ, Silver J |title=Polio voices: an oral history from the American polio epidemics and worldwide eradication efforts |publisher=Praeger |location=New York |year=2007 |isbn=978-0-275-99492-1 |url= https://books.google.com/books?id=RomvGee67tUC&q=polio }}

* Zimmermann, Jonas. "War on Disease: Polio Eradication in the United States." ''Historia. scriber'' 15 (2023): 263-280. [https://scribere.at/historia_scribere/article/download/4106/3017 online]

== External links ==
{{portal|Medicine|Viruses}}
* {{commons category-inline|Polio}}
* {{wikiquote-inline}}
* {{wiktionary-inline}}

{{Medical resources
|ICD11          = {{ICD11|1C81}} (acute), {{ICD11|1G83}} (sequelae), {{ICD11|XN3M0}} (viruses)
|ICD10          = {{ICD10|A80}} (acute), {{ICD10|B91}} (sequelae)
|ICD9           = {{ICD9|045}} (acute), {{ICD9|138}} (sequelae)
|DiseasesDB     = 10209
|MedlinePlus    = 001402
|eMedicineSubj  = ped
|eMedicineTopic = 1843
|eMedicine_mult = {{eMedicine2|pmr|6}}
|MeshName       = Poliomyelitis
|MeshNumber     = C02.182.600.700
}}
{{Viral diseases}}
{{CNS diseases of the nervous system}}
{{Eradication of infectious disease}}
{{Authority control}}

[[Category:Polio| ]]
[[Category:Wikipedia medicine articles ready to translate]]
[[Category:Wikipedia infectious disease articles ready to translate]]
[[Category:Vaccine-preventable diseases]]
[[Category:Central nervous system disorders]]
[[Category:Myelin disorders]]