Editing Polio (section)

=== 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 |url=http://pediatrics.aappublications.org/cgi/content/full/99/2/300 |url-status=live |journal=Pediatrics |volume=99 |issue=2 |pages=300–305 |date=February 1997 |archive-url=https://web.archive.org/web/20070930165356/http://pediatrics.aappublications.org/cgi/content/full/99/2/300 |archive-date=30 September 2007 |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" />