Polio vaccine
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/* The "great race" */ fix typo
Two '''polio [[vaccine]]s''' are used throughout the world to combat [[polio]]. The first was developed by [[Jonas Salk]], first tested in 1952, and announced to the world by Salk on [[April 12]], [[1955]]. It consists of an injected dose of inactivated (dead) [[poliovirus]]. The second was an oral vaccine developed by [[Albert Sabin]] using [[Attenuated virus|attenuated]] poliovirus that he had received from [[Hilary Koprowski]]. [[Clinical trial|Human trials]] of Sabin's vaccine began in 1957 and it was licensed in 1962.<ref>{{cite web | title = A Science Odyssey: People and Discoveries | publisher = PBS | year = 1998 | url = http://www.pbs.org/wgbh/aso/databank/entries/dm52sa.html | accessdate = 2007-08-14}}</ref> The two vaccines have [[Poliomyelitis eradication|eradicated polio]] from most of the countries in the world<ref name=Aylward_2006>{{cite journal |author=Aylward R |title=Eradicating polio: today's challenges and tomorrow's legacy |journal=Ann Trop Med Parasitol |volume=100 |issue=5-6 |pages=401–13 |year=2006 |pmid=16899145 |doi=10.1179/136485906X97354}}</ref><ref>{{cite journal |author=Schonberger L, Kaplan J, Kim-Farley R, Moore M, Eddins D, Hatch M |title=Control of paralytic poliomyelitis in the United States |journal=Rev. Infect. Dis. |volume=6 Suppl 2 |issue= |pages=S424–6 |year=1984 |pmid=6740085}}</ref> and reduced the worldwide incidence from an estimated 350,000 cases in 1988 to just over 1000 cases in 2007.<ref name=eradication>{{cite journal |author= |title=Update on vaccine-derived polioviruses |journal=MMWR Morb Mortal Wkly Rep |volume=55 |issue=40 |pages=1093–7 |year=2006 |pmid=17035927}}</ref><ref name=Kew_2005>{{cite journal |author=Kew O, Sutter R, de Gourville E, Dowdle W, Pallansch M |title=Vaccine-derived polioviruses and the endgame strategy for global polio eradication |journal=Annu Rev Microbiol |volume=59 |issue= |pages=587–635 |year=2005 |pmid=16153180 |doi=10.1146/annurev.micro.58.030603.123625}}</ref><ref>{{cite web | title = Wild Poliovirus Weekly Update | publisher = CDC, WHO, Rotary International, UNICEF | year = 2008 | url = http://www.polioeradication.org/casecount.asp| accessdate = 2008-01-18}}</ref>
== The "great race" ==
In 1936 Maurice Brodie, a research assistant at [[New York University]], attempted to produce a [[formaldehyde]]-killed polio vaccine from ground-up monkey spinal cords. His initial attempts were hampered by the difficulty of obtaining enough virus. Brodie first tested the vaccine on himself and several of his assistants. He then gave the vaccine to three thousand children: many developed allergic reactions, but none developed immunity to polio.<ref name = Pearce>{{cite journal |author=Pearce J |title=Salk and Sabin: poliomyelitis immunisation |url= http://jnnp.bmj.com/cgi/content/full/75/11/1552 |journal=J Neurol Neurosurg Psychiatry |volume=75 |issue=11 |pages=1552 |year=2004 |pmid = 15489385 |doi=10.1136/jnnp.2003.028530}}</ref> Philadelphia pathologist John Kollmer also claimed to have developed a vaccine that same year, but it too produced no immunity and was blamed for causing a number of cases, some of them fatal.<ref name=Rainsberger>{{cite web | author=Rainsberger M | title=More than a March of Dimes | publisher=The University of Texas at Austin | url=http://www.utexas.edu/features/2005/polio/ | accessdate=2007-01-29}}</ref>
[[Image:Polio immunization days PHIL 2445.png|thumb|300px|left|Mass polio vaccination in [[Columbus, Georgia]] during the early days of the National Polio Immunization Program.]]
A breakthrough came in 1948 when a research group headed by [[John Enders]] at the [[Children's Hospital Boston]] successfully cultivated the [[poliovirus]] in human tissue in the laboratory.<ref name=Enders>{{cite journal |author=Enders JF, Weller TH, Robbins FC |title=Cultivation of the Lansing Strain of Poliomyelitis Virus in Cultures of Various Human Embryonic Tissues |doi= 10.1126/science.109.2822.85 |journal=Science |volume=109 |issue=2822 |pages=85–87 |year=1949 |pmid=17794160 }}</ref> This development greatly facilitated vaccine research and ultimately allowed for the development of vaccines against polio. Enders and his colleagues, [[Thomas H. Weller]] and [[Frederick C. Robbins]], were recognized for their labors with a [[Nobel Prize in Physiology or Medicine]] in 1954.<ref name=Nobel_1954>{{cite web | title=The Nobel Prize in Physiology or Medicine 1954 | publisher=The Nobel Foundation | url=http://nobelprize.org/nobel_prizes/medicine/laureates/1954/ | accessdate=2007-01-29}}</ref> Other important advancements that lead to the development of polio vaccines were: the identification of three poliovirus serotypes (Poliovirus type 1 (PV1 or Mahoney), PV2 (Lansing), and PV3 (Leon)), the finding that preceding paralysis, the virus must be present in the blood, and the demonstration that administration of antibodies in the form of gamma-globulin protects against paralytic polio.<ref name=Kew_2005/><ref>{{cite journal |author=Hammon W, Coriell L, Wehrle P, Stokes J |title=Evaluation of Red Cross gamma globulin as a prophylactic agent for poliomyelitis. IV. Final report of results based on clinical diagnoses |journal=J Am Med Assoc |volume=151 |issue=15 |pages=1272–85 |year=1953 |pmid=13034471}}</ref>
In 1952 and 1953, the U.S. experienced an outbreak of 58,000 and 35,000 polio cases, respectively, up from a typical number of some 20,000 cases a year. Amid this U.S. polio epidemic, millions of dollars were invested in finding and marketing a polio vaccine by commercial interests, including Lederle Laboratories in New York under the direction of [[H. R. Cox]].
Polish-born virologist and immunologist [[Hilary Koprowski]], who also worked at Lederle, claims to have created the first successful polio vaccine (in 1950) but his vaccine, a live attenuated virus taken orally, was still in the research stage and would not be ready for use until five years after Jonas Salk's polio vaccine (a dead injectable vaccine) reached the market.
The samples of difficult-to-manufacture attenuated virus that [[Albert Sabin]] used to develop his oral polio vaccine were given to him by [[Hilary Koprowski]]. "Koprowski would later complain that the polio vaccine he had discovered became known as the Sabin vaccine."<ref name = Sanofi>{{cite web | title = Competition to develop an oral vaccine | work = Conquering Polio | publisher = [[Sanofi Pasteur]] SA | date = 2007-02-02 | url = http://www.polio.info/polio-eradication/front/templates/index.jsp?siteCode=POLIO&codeRubrique=34&lang=EN | accessdate = 2007-03-12}}</ref> Koprowski's own vaccine was ultimately tested, but the outcome was a failure. After the attenuated live virus entered the body, it sometimes reverted to a [[virulent]] state.<ref name=Dick>{{cite journal |author=Dick GWA, Dane DS |title=Vaccination Against Poliomyelitis with Live Virus Vaccines 3. The Evaluation of TN and SM Virus Vaccines |url= http://www.pubmedcentral.nih.gov/pagerender.fcgi?tool=pmcentrez&artid=1974029&pageindex=1 |journal=British Medical Journal |volume=1 |issue=5010 |pages=71–74 |year=1957 |pmid=13383193 }}</ref><ref name=Lindner_2006>{{cite journal |author=Lindner U, Blume S |title=Vaccine innovation and adoption: polio vaccines in the UK, the Netherlands and West Germany, 1955-1965 |url= http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1592614 |journal=Med Hist |volume=50 |issue=4 |pages=425–46 |year=2006 |pmid=17066127 }}</ref> Nevertheless, from 1957 to 1960, large-scale tests were carried out in the [[Zaire|Congo]]. The results have been controversial,<ref name=Collins_2000>{{cite news | last = Collins | first = Huntly | title = The Gulp Heard Round the World | pages = Section D, page 1 | publisher = Philadelphia Inquirer | date = [[2000-11-06]] | url = http://www.koprowski.net/Polio%20Article.htm | accessdate = 2007-02-06 }}</ref> and [[OPV AIDS hypothesis|accusations in the 1990s]] arose that the vaccine created the conditions necessary for the transmission of [[SIV]] from [[chimpanzee]]s to humans, causing [[HIV/AIDS]]. This hypothesis has, however, [[Hilary Koprowski#Hypothesis refuted|been refuted]].
The development of two polio vaccines led to the first modern mass [[inoculation]]s. The last cases of paralytic poliomyelitis caused by endemic transmission of [[wild virus]] in the United States were in 1979, when an outbreak occurred among the [[Amish]] in several [[Midwest]] states.<ref name = PinkPages>{{cite book | author = Atkinson W, Hamborsky J, McIntyre L, Wolfe S, eds. | title = Epidemiology and Prevention of Vaccine-Preventable Diseases (The Pink Book) | edition = 10th ed. | publisher = Washington DC: Public Health Foundation | year = 2007 | url = http://www.cdc.gov/nip/publications/pink/polio.pdf | accessdate = 2007-03-12}}</ref> The disease was entirely eradicated in [[the Americas]] by 1994.<ref name=MMWR_1994>{{cite journal| author= | title = International Notes Certification of Poliomyelitis Eradication – the Americas, 1994 | journal = Morbidity and Mortality Weekly Report | publisher = Centers for Disease Control and Prevention | volume= 43 | issue= 39 | pages = 720–722 | year=1994 | url = http://www.cdc.gov/mmwr/preview/mmwrhtml/00032760.htm | pmid = 7522302 }}</ref>
=== Salk's "inactivated polio vaccine" ===
The first effective polio vaccine was developed in 1952 by [[Jonas Salk]] at the [[University of Pittsburgh]]. The Salk vaccine, or ''inactivated poliovirus vaccine'' (IPV), is based on three wild, [[virulent]] reference strains, Mahoney (type 1 poliovirus), MEF-1 (type 2 poliovirus), and Saukett (type 3 poliovirus), grown in a type of monkey [[kidney]] tissue culture ([[Vero cell]] line), which are then inactivated with [[formalin]].<ref name=Kew_2005/> The injected Salk vaccine confers [[IgG]]-mediated immunity in the bloodstream, which prevents polio infection from progressing to [[viremia]] and protects the [[motor neurons]], thus eliminating the risk of bulbar polio and [[post-polio syndrome]]. However, because it offers no protection to the mucosal lining of the intestine, people vaccinated with Salk's vaccine can still carry the disease and spread it to unvaccinated individuals.
In 1954, the vaccine was tested at Arsenal Elementary School and the [[D. T. Watson Home for Crippled Children|Watson Home for Children]] in [[Pittsburgh, Pennsylvania]]. Salk's vaccine was then used in a test called the Francis Field Trial, led by [[Thomas Francis]]; the largest medical experiment in history. The test began with some 4,000 children at Franklin Sherman Elementary School in [[McLean, Virginia]], and would eventually involve 1.8 million children, in 44 states from [[Maine]] to [[California]].<ref name=MoD_2004>{{cite web | title = Polio Victory Remembered as March of Dimes Marks 50th Anniversary of Salk Vaccine Field Trials | work = News Desk | url = http://www.marchofdimes.com/aboutus/10651_11681.asp | date = 2004-04-26 | accessdate = 2007-03-12}}</ref> By the conclusion of the study, roughly 440,000 received one or more injections of the vaccine, about 210,000 children received a [[placebo]], consisting of harmless [[culture media]], and 1.2 million children received no vaccination and served as a control group, who would then be observed to see if any contracted polio.<ref name = Sanofi/> The results of the field trial were announced [[April 12]], [[1955]] (the tenth anniversary of the death of Franklin Roosevelt). The Salk vaccine had been 60 - 70% effective against PV1 (poliovirus type 1), over 90% effective against PV2 and PV3, and 94% effective against the development of bulbar polio.<ref name=Smith_1990>{{cite book |last = Smith | first = Jane S. | title = Patenting the Sun: Polio and the Salk Vaccine | publisher = William Morrow & Co |year= 1990 |isbn=0-688-09494-5}}</ref> Soon after Salk's vaccine was licensed in 1955 children's vaccination campaigns were launched. In the U.S, following a mass immunization campaign promoted by the [[March of Dimes]], the annual number of polio cases fell to 5,600 by 1957.<ref name= Sass>{{cite book |author=[edited by] Edmund J. Sass with George Gottfried, Anthony Sorem; foreword by Richard Owen |title=Polio's legacy: an oral history |publisher=University Press of America |location=Washington, D.C. |year=1996 |isbn=0-7618-0144-8 |url=http://www.cloudnet.com/~edrbsass/poliotimeline.htm '''Summary'''}}</ref> The IPV vaccine was used extensively in the U.S. until the early 1960s. An enhanced-[[potency]] IPV was licensed in the United States in November 1987, and is currently the vaccine of choice in the United States.<ref name = PinkPages/>
[[Image:Polio vaccine poster.jpg|thumb|This 1963 poster featured CDC’s national symbol of [[public health]], the "Wellbee", encouraging the public to receive an oral polio vaccine.]]
=== Sabin's "oral polio vaccine" ===
Eight years after Salk's success, [[Albert Sabin]] developed the oral polio vaccine (OPV).<ref>{{cite journal |author=Sabin A, Ramos-Alvarez M, Alvarez-Amezquita J, Pelon W, Michaels R, Spigland I, Koch M, Barnes J, Rhim J |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= |pages=1521–6 |year= |pmid = 14440553}}</ref> The OPV is a live-[[attenuated]] vaccine, produced by the passage of the virus through non-human cells at a sub-[[physiological]] temperature, which produces spontaneous mutations in the viral genome.
There are 57 [[nucleotide]] substitutions which distinguish the attenuated Sabin 1 strain from its virulent parent (the Mahoney serotype), two nucleotide substitutions attenuate the Sabin 2 strain, and 10 substitutions are involved in attenuating the Sabin 3 strain.<ref name=Kew_2005/> The primary attenuating factor common to all three Sabin vaccines is a mutation located in the virus's internal ribosome entry site (or [[IRES]])<ref name= Chan>Charles Chan and Roberto Neisa. [http://www.brown.edu/Courses/Bio_160/Projects2000/Polio/TableofContents.html "Poliomyelitis".] Brown University.</ref> which alters [[stem-loop]] structures, and reduces the ability of poliovirus to translate its RNA template within the host cell.<ref>{{cite journal |author=Gromeier M, Bossert B, Arita M, Nomoto A, Wimmer E |title=Dual stem loops within the poliovirus internal ribosomal entry site control neurovirulence |url= http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pubmed&pubmedid=9882296 |journal=J Virol |volume=73 |issue=2 |pages=958–64 |year=1999 |pmid=9882296}}</ref>
The attenuated poliovirus in the Sabin vaccine replicates very efficiently in the gut, the primary site of infection and replication, but is unable to replicate efficiently within [[nervous system]] tissue. The OPV proved to be superior in administration, and also provided longer lasting [[immunity (medical)|immunity]] than the Salk vaccine.<ref name= Chan/> Although Salk's vaccine had reduced the incidence of polio to a tiny fraction of what it was in the early 1950s, it was the oral live-virus vaccine that enabled the complete elimination of the wild polio virus in the [[United States]].
In 1961, type 1 and 2 [[monovalent]] oral poliovirus vaccine (MOPV) was licensed, and in 1962, type 3 MOPV was licensed. In 1963, trivalent OPV was licensed, and became the vaccine of choice in the United States and most other countries of the world, largely replacing the inactivated polio vaccine.<ref name = Pearce/> A second wave of mass immunizations led to a further dramatic decline in the number of polio cases. In 1961, only 161 cases were recorded in the United States.<ref name= Hinman>{{cite journal |author=Hinman A |title=Landmark perspective: Mass vaccination against polio |journal=JAMA |volume=251 |issue=22 |pages=2994–6 |year=1984 |pmid = 6371280 |doi=10.1001/jama.251.22.2994}}</ref>
== Iatrogenic (vaccine-induced) polio ==
A major concern attributable to the oral polio vaccine (OPV) is that it can revert to a virulent form.<ref name=Shimizu_2004>{{cite journal | author = Shimizu H, ''et al'' | title = Circulation of type 1 vaccine-derived poliovirus in the Philippines in 2001. | url= http://jvi.asm.org/cgi/content/full/78/24/13512?view=long&pmid=15564462 | journal = J Virol | volume = 78 | issue = 24 | pages = 13512–21 | year = 2004 | pmid = 15564462 | doi = 10.1128/JVI.78.24.13512-13521.2004}}</ref> Clinical disease caused by vaccine-derived poliovirus (VDPV) is indistinguishable from that caused by wild polioviruses.<ref name= Cono>Cono, Joanne and Lorraine N. Alexander. (2002). VPD (Vaccine Preventable Disease) Surveillance Manual, 3rd Edition, [http://www.cdc.gov/nip/publications/surv-manual/chpt10_polio.pdf Chapter 10, Poliomyelitis] p.10-1.</ref> This is believed to be a rare event, but outbreaks of vaccine-derived poliovirus (VDPV) have been reported, and tend to occur in areas of low coverage by OPV, presumably because the OPV is itself protective against the related outbreak strain.<ref name=Kew_2002>{{cite journal | author = Kew O, ''et al'' | title = Outbreak of poliomyelitis in Hispaniola associated with circulating type 1 vaccine-derived poliovirus. | journal = Science | volume = 296 | issue = 5566 | pages = 356–9 | year = 2002 | pmid = 11896235 | doi = 10.1126/science.1068284}}</ref><ref name=Yang_2003>{{cite journal | author = Yang C, Naguib T, Yang S, Nasr E, Jorba J, Ahmed N, Campagnoli R, van der Avoort H, Shimizu H, Yoneyama T, Miyamura T, Pallansch M, Kew O | title = Circulation of endemic type 2 vaccine-derived poliovirus in Egypt from 1983 to 1993. | journal = J Virol | volume = 77 | issue = 15 | pages = 8366–77 | year = 2003 | pmid = 12857906 | doi = 10.1128/JVI.77.15.8366-8377.2003}}</ref> Reversion is not possible in IPV vaccinations used in the U.S., and thus vaccine-induced polio is not a concern.
The rate of vaccine-associated paralytic poliomyelitis (VAPP) varies by region but is generally about 1 case per 750,000 vaccine recipients.<ref name=Racaniello_2006>{{cite journal |author=Racaniello V |title=One hundred years of poliovirus pathogenesis |journal=Virology |volume=344 |issue=1 |pages=9–16 |year=2006 |pmid=16364730 |doi=10.1016/j.virol.2005.09.015}}</ref> VAPP is more likely to occur in adults than in children. In [[immunodeficient]] children, the risk of VAPP is almost 7,000 times higher, particularly for persons with [[B-lymphocyte]] disorders (e.g., [[agammaglobulinemia]] and [[hypogammaglobulinemia]]), which reduce the synthesis of protective [[antibodies]].<ref name= Cono/> The [[World Health Organization]] considers the benefits of vaccination to far outweigh the risk of vaccine derived polio. Outbreaks of vaccine derived polio have been stopped by multiple rounds of high-quality vaccination, in order to immunize the entire population.<ref name="who-Q&A">{{cite web | title = What is vaccine-derived polio? | publisher = WHO | date = 8 October 2007 | url = http://www.who.int/features/qa/64/en/index.html}}</ref>
Outbreaks of VAPP occurred independently in [[Belarus]] (1965–66), [[Egypt]] (1983–1993), [[Hispaniola]] (2000–2001), [[Philippines]] (2001), [[Madagascar]] (2001–2002),<ref>{{cite journal |author=Kew O, Wright P, Agol V, Delpeyroux F, Shimizu H, Nathanson N, Pallansch M |title=Circulating vaccine-derived polioviruses: current state of knowledge |url= http://www.scielosp.org/scielo.php?script=sci_arttext&pid=S0042-96862004000100006&lng=en&nrm=iso&tlng=en| journal=Bull World Health Organ |volume=82 |issue=1 |pages=16–23 |year=2004 |pmid=15106296 }}</ref> and in [[Haiti]] (2002), where political strife and poverty have interfered with vaccination efforts.<ref>Fox, Maggie
[http://www.vaccinationnews.com/DailyNews/March2002/PolioHaitiLinkedIncompleteVax.htm Polio in Haiti linked to incomplete vaccinations] Reuters</ref> In 2006 an outbreak of vaccine-derived poliovirus occurred in [[China]].<ref name=Liang_2006>{{cite journal | author = Liang X, Zhang Y, Xu W, Wen N, Zuo S, Lee L, Yu J | title = An outbreak of poliomyelitis caused by type 1 vaccine-derived poliovirus in China | journal = J Infect Dis | volume = 194 | issue = 5 | pages = 545–51 | year = 2006 | pmid = 16897650 | doi = 10.1086/506359}}</ref> Cases have been reported from [[Cambodia]] (2005-2006), [[Myanmar]] (2006-2007), Iran (1995, 2005-2007), Syria, Kuwait and Egypt, while in northern Nigeria, 69 cases were reported in 2007.<ref>{{citation | title = Update on Vaccine-Derived Polioviruses --- Worldwide, January 2006–August 2007 | journal = Morbidity and Mortality Weekly Report | date =September 28 | year = 2007 | volume = 56 | number = 38 | pages =996–1001 | publisher = Centers for Disease Control and Prevention | url = http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5638a3.htm?s_cid=mm5638a3_e}}</ref>
== Vaccination schedule ==
[[Image:Poliodrops.jpg|thumb|right|A child receives oral polio vaccine.]]
Following the widespread use of poliovirus vaccine in the mid-1950s, the incidence of poliomyelitis declined rapidly in many industrialized countries. As the incidence of wild polio diminishes, nations transition from use of the oral vaccine back to the injected vaccine because the risk of iatrogenic polio outweighs the risk of subclinical transmission.
The use of OPV was discontinued in the United States in 2000, but it continues to be used around the globe.<ref name= PinkPages/> In 2002, a [[pentavalent]] (5-component) combination vaccine (called Pediarix) containing IPV was approved for use in the United States. The vaccine also contains combined [[diphtheria]], [[tetanus]], and [[acellular]] [[pertussis]] vaccines ([[DTaP]]) and a pediatric dose of [[hepatitis B]] vaccine.<ref name = PinkPages/> In the UK the change from OPV to IPV occurred in 2004 and for convenience polio vaccine was combined with tetanus, diphtheria, pertussis and ''[[Haemophilus influenzae]]'' type b vaccines.<ref name=UK>{{cite book |author=Joint Committee on Vaccination and Immunisation, David Salisbury (Editor), Mary Ramsay (Editor), Karen Noakes (Editor) |title=Immunisation Against Infectious Disease 2006 Chapter 26:Poliomyelitis | url=http://www.immunisation.nhs.uk/files/GB_26_polio.pdf |publisher=Stationery Office |location=Edinburgh |year= |pages=313-329|isbn=0-11-322528-8 }}</ref>
The first dose of polio vaccine is given shortly after birth, usually between 1-2 months of age, a second dose is given at 4 months of age.<ref name= PinkPages/> The timing of the third dose depends on the vaccine formulation but should be given between 6–18 months of age.<ref name=UK/> Booster vaccination are given at 4 to 6 years of age, for a total of four doses at or before school entry.<ref name=Peds>{{cite journal |author= |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 |journal=Pediatrics |volume=99 |issue=2 |pages=300–5 |year=1997 |pmid=9024465|doi=10.1542/peds.99.2.300}}</ref> In some countries a fifth vaccination is given during [[adolescence]].<ref name=UK/> Routine vaccination of adults (18 years of age and older) in developed countries is neither necessary nor recommended because most adults are already immune and have a very small risk of exposure to wild poliovirus in their home countries.<ref name= PinkPages/>
== Efficacy ==
In the generic sense, vaccination works by priming the [[immune system]] with an '[[immunogen]]'. Stimulating immune response, via use of an infectious agent, is known as [[immunization]]. Vaccine [[efficacy]] is defined by the amount of [[immunity (medical)|immunity]] against infection a particular vaccine provides, and is often measured by detection of protective [[antibodies]] in the blood.<ref name=Fedson_1998>{{cite journal |author=Fedson D |title=Measuring protection: efficacy versus effectiveness |journal=Dev Biol Stand |volume=95 |pages=195–201 |year=1998 |pmid=9855432 }}</ref>
The development of immunity to polio efficiently blocks person-to-person transmission of wild poliovirus, thereby protecting both individual vaccine recipients and the wider community.<ref name=Fine>{{cite journal |author=Fine P, Carneiro I |title=Transmissibility and persistence of oral polio vaccine viruses: implications for the global poliomyelitis eradication initiative |url= http://aje.oxfordjournals.org/cgi/reprint/150/10/1001| journal=Am J Epidemiol |volume=150 |issue=10 |pages=1001–21 |year=1999 |pmid=10568615}}</ref> Because there is no long term [[asymptomatic carrier|carrier]] state for poliovirus in immunocompetent individuals, polioviruses have no non-primate reservoir in nature, and survival of the virus in the environment for an extended period of times appears to be remote, interruption of person-to person transmission of the virus by vaccination is the critical step in global polio eradication.<ref name=Fine/>
After two doses of inactivated polio vaccine (IPV), ninety percent or more of individuals develop protective antibody to all three [[serotype]]s of poliovirus, and at least 99% are immune to poliovirus following three doses. A single dose of oral polio vaccince produces immunity to all three poliovirus serotypes in approximately 50% of recipients.<ref name=PinkPages/> Three doses of live-attenuated OPV produce protective antibody to all three poliovirus types in more than 95% of recipients. OPV produces excellent immunity in the [[intestine]], the primary site of wild poliovirus entry, which helps prevent infection with wild virus in areas where the virus is [[endemic (epidemiology)|endemic]].<ref name=Peds/> IPV produces less [[gastrointestinal]] immunity than does OPV, so persons who receive IPV are more easily infected with wild poliovirus. In regions without wild poliovirus, inactivated polio vaccine is the vaccine of choice.<ref name=Peds/> In regions with higher incidence of polio, and thus a different relative risk between efficacy and reversion of the vaccine to a virulent form, live vaccine is still used. The live virus also has stringent requirements for transport and storage, which are a problem in some hot or remote areas.
As with other live-virus vaccines, immunity initiated by OPV is probably lifelong. The duration of immunity induced by IPV is not known with certainty, although a complete series is thought to provide protection for many years.<ref name=Robertson_1993>{{cite web | last = Robertson | first = Susan | title = Module 6: Poliomyelitis | work = The Immunological Basis for Immunization Series | publisher = [[World Health Organization]] (Geneva, Switzerland) | url = http://www.who.int/vaccines-documents/DocsPDF-IBI-e/mod6_e.pdf | accessdate = 2007-03-12}}</ref>
== Contamination concerns ==
In 1960, it was determined that the [[rhesus monkey]] kidney cells used to prepare the poliovirus vaccines were infected with a virus called [[SV40]] (or Simian Virus-40).<ref name=SV>{{cite web| title = Simian Virus 40 (SV40), Polio Vaccine, and Cancer | work =| publisher = Centers for Disease Control| date = April 22, 2004 | url = http://www.cdc.gov/nip/vacsafe/concerns/cancer/default.htm | accessdate = 2007-02-03 }}</ref> SV40, also discovered in 1960, is a naturally occurring [[virus]] that infects monkeys. In 1961, SV40 was found to cause tumors in [[rodent]]s.<ref name=Eddy_1961>{{cite journal |author=Eddy B, Borman G, Berkeley W, Young R |title=Tumors induced in hamsters by injection of rhesus monkey kidney cell extracts |journal=Proc Soc Exp Biol Med |volume=107 |issue= |pages=191–7 |year = 1961 |pmid = 13725644}}</ref> More recently, the virus was found in certain forms of [[cancer]] in humans, for instance [[brain tumor|brain]] and [[bone tumor]]s, [[mesothelioma]]s, and some types of [[non-Hodgkin's lymphoma]].<ref>{{cite journal |author=Carbone M |title=Simian virus 40 and human tumors: It is time to study mechanisms |journal=J Cell Biochem |volume=76 |issue=2 |pages=189–93 |year=1999 |pmid = 10618636 |doi=10.1002/(SICI)1097-4644(20000201)76:2<189::AID-JCB3>3.0.CO;2-J}}</ref><ref>{{cite journal |author=Vilchez R, Kozinetz C, Arrington A, Madden C, Butel J |title=Simian virus 40 in human cancers |journal=Am J Med |volume=114 |issue=8 |pages=675–84 |year=2003 |pmid=12798456 |doi=10.1016/S0002-9343(03)00087-1}}</ref> However, it has not been determined that SV40 causes these cancers.<ref name= Engels>{{cite journal |author=Engels E |title=Cancer risk associated with receipt of vaccines contaminated with simian virus 40: epidemiologic research |url=http://dceg.cancer.gov/pdfs/engels41972005.pdf |journal=Expert Rev Vaccines |volume=4 |issue=2 |pages=197–206 |year=2005 |pmid=15889993 |doi=10.1586/14760584.4.2.197}}</ref>
SV40 was found to be present in stocks of the injected form of the polio vaccine (IPV) in use between 1954 to 1962.{{Fact|date=March 2008}} It is not found in the OPV form (which was licensed later).{{Fact|date=March 2008}} Over 98 million Americans received one or more doses of polio vaccine between 1955 to 1963 when a proportion of vaccine was contaminated with SV40; it has been estimated that 10 - 30 million Americans may have received a dose of vaccine contaminated with SV40.<ref name=SV/> Later analysis suggested that vaccines produced by the former [[Soviet bloc]] countries until 1980, and used in the [[USSR]], [[China]], [[Japan]], and several [[Africa]]n countries, may have been contaminated; meaning hundreds of millions more may have been exposed to SV40.<ref>{{cite web|last= Debbie Bookchin| title = Vaccine scandal revives cancer fear | publisher = New Scientist | date = 7 July 2004 | url = http://www.newscientist.com/news/news.jsp?id=ns99996116| accessdate = 2007-02-03 }}</ref>
In 1998, the [[National Cancer Institute]] undertook a large study, using cancer case information from the Institutes SEER database. The published findings from the study revealed that there was no increased incidence of cancer in persons who may have received vaccine containing SV40.<ref name=Strickler_1998>{{cite journal |author=Strickler H, Rosenberg P, Devesa S, Hertel J, Fraumeni J, Goedert J |title=Contamination of poliovirus vaccines with simian virus 40 (1955-1963) and subsequent cancer rates |journal=JAMA |volume=279 |issue=4 |pages=292–5 |year=1998 |pmid=9450713 |doi=10.1001/jama.279.4.292}}</ref> Another large study in Sweden examined cancer rates of 700,000 individuals who had received potentially contaminated polio vaccine as late as 1957; the study again revealed no increased cancer incidence between persons who received polio vaccines containing SV40 and those who did not.<ref name=Olin_1998>{{cite journal |author=Olin P, Giesecke J |title=Potential exposure to SV40 in polio vaccines used in Sweden during 1957: no impact on cancer incidence rates 1960 to 1993 |journal=Dev Biol Stand |volume=94 |issue= |pages=227–33 |year=1998 |pmid=9776244}}</ref> The question of whether SV40 causes cancer in humans remains controversial however, and the development of improved assays for detection of SV40 in human tissues will be needed to resolve the controversy.<ref name= Engels/>
== Efforts towards polio eradication ==
{{details|Poliomyelitis eradication}}
Following the widespread use of polio vaccines in the mid-1950s, the incidence of poliomyelitis declined dramatically in many industrialized countries. A global effort to eradicate polio, led by the [[World Health Organization]], [[UNICEF]], and [[The Rotary Foundation]], began in 1988 and has relied largely on the oral polio vaccine developed by [[Albert Sabin]].<ref name= Watch>{{cite web| last = Mastny| first = Lisa | title = Eradicating Polio: A Model for International Cooperation |publisher = Worldwatch Institute | date = [[January 25]], [[1999]] | url = http://www.worldwatch.org/node/1644 | accessdate = 2007-02-02}}</ref> If this long-term public-health goal is achieved, poliomyelitis would join [[smallpox]] as only the second infectious disease of humans to be eradicated worldwide, and should make subsequent polio vaccinations unnecessary.
By 2004, cases of poliomyelitis in Africa had been reduced to just a small number in isolated regions of in the western portion of the continent, with sporadic cases elsewhere. However, recent opposition to vaccination campaigns have evolved,<ref>[http://news.bbc.co.uk/2/hi/africa/2070634.stm Nigeria Muslims oppose polio vaccination] ''BBC News'' [[27 June]] [[2002]]</ref><ref>[http://www.nytimes.com/2006/03/20/international/asia/20polio.html?pagewanted=2 Rumor, Fear and Fatigue Hinder Final Push to End Polio] Celia W. Dugger and Donald G. McNeil Jr. ''New York Times'' [[March 20]], [[2006]]</ref> often relating to fears that the vaccine might induce [[sterility]].<ref name=BBC>BBC News [http://news.bbc.co.uk/2/hi/africa/4539757.stm "Anti-polio vaccine Malians jailed"] [[12 May]] [[2005]]</ref> The disease has since resurged in [[Nigeria]] and in several other African nations, which some [[epidemiologist]]s cite is due to refusals by certain local populations to allow their children to receive the polio vaccine.<ref name=Jegede>{{cite journal |author=Jegede AS |title=What led to the Nigerian boycott of the polio vaccination campaign? |doi= 10.1371/journal.pmed.0040073| journal=PLoS Med. |volume=4 |issue=3 |pages=e73 |year=2007 |pmid=17388657}}</ref> Some public-health workers argue that debates relating to the [[OPV AIDS hypothesis]] have further fueled vaccination fears among contemporary Africans.<ref name=Hooper1>Cohen, Jon (2000) [http://www.theatlantic.com/doc/200010/origin-aids "The Hunt for the Origin of AIDS"] ''Atlantic Monthly'' (Oct), p. 104; see also response [http://www.aidsorigins.com/content/view/128/49/]</ref>
Polio is also endemic in areas of India and Pakistan, and has again spread into Bangladesh.<ref name=GPEI>Global Polio Eradication Initiative (2007) [http://www.polioeradication.org/content/general/casemap.shtml Map of last six months of polio cases worldwide] ''Wild Poliovirus Weekly Update'' initiative of WHO, CDC, UNICEF, Rotary International</ref><ref name=BBC2>BBC News (2007) [http://news.bbc.co.uk/2/hi/south_asia/6412835.stm "Bangladesh begins new polio drive]</ref> Recent studies by the [[Indian Medical Association]] suggest that some OPV preparations currently in use there are inducing vaccine-associated paralytic poliomyelitis (VAPP) among vaccine recipients at rates not before seen in prior vaccination campaigns,<ref name=Hindu>Puliyel JM (2006) [http://www.hindu.com/mag/2006/11/19/stories/2006111900100400.htm "Lessons from the polio campaign"]''The Hindu'', Sunday Magazine ([[November 19]])</ref> with at least 70 confirmed cases of vaccine-derived disease in Nigeria in 2006,<ref name=NatMed1>{{cite journal |author=Willyard C |title=Polio eradication campaign copes with unusual outbreak |journal=Nat. Med. |volume=13 |issue=12 |pages=1394 |year=2007 |pmid=18064018 |doi=10.1038/nm1207-1394}}</ref> and at least 1600 cases in India.<ref name=NatMed>{{cite journal |author=Bhasin VK |title=Problems with the oral polio vaccine |journal=Nat. Med. |volume=14 |issue=1 |pages=9 |year=2008 |pmid=18180708 |doi=10.1038/nm0108-9}}</ref> Although the exact cause of this vaccine-derived outbreak has not been determined, at least some public-health authorities in India are recommending discontinuing use of live-virus OPV in favor of more costly IPV in future polio eradication efforts there.<ref name=NatMed/>
== See also ==
* [[Hilary Koprowski]]
* [[Mathematical modelling in epidemiology#The mathematics of mass vaccination|The mathematics of mass vaccination]]
* [[Herd immunity]]
* [[March of Dimes]]
== References ==
{{Reflist|2}}
== External links ==
* [http://blogs.cgdev.org/vaccine CGDev.org] - 'Vaccines for Development', [[Center for Global Development]]
* [http://www.pbs.org/wgbh/aso/databank/entries/dm52sa.html PBS.org] - 'People and Discoveries: Salk Produces Polio Vaccine 1952', [[PBS]]
* [http://www.sfgate.com/cgi-bin/article.cgi?file=/chronicle/archive/2001/07/15/MN193825.DTL SFGate.com] - 'Rogue virus in the vaccine: Early polio vaccine harbored virus now feared to cause cancer in humans', William Carlsen, ''[[San Francisco Chronicle]]'' ([[July 15]], [[2001]])
{{Vaccines}}
[[Category:Poliomyelitis]]
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[[Category:Live vaccines]]
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