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USA Since 1980 - 1992 zero wild polio cases - but 80 cases polio from the vaccine itself.
Epidemiology of poliomyelitis in the United States one decade after the last reported case of indigenous wild virus
"We reviewed national surveillance data on poliomyelitis for 1960-1989 to assess the changing risks of wild-virus, vaccine-associated, and imported paralytic disease; we also sought to characterize the epidemiology of poliomyelitis for the period 1980-1989. The risk of VAPP has remained exceedingly low but stable since the mid-1960s, with approximately 1 case occurring per 2.5 million doses of oral poliovirus vaccine (OPV) distributed during 1980-1989. Since 1980 no indigenous cases of wild-virus disease, 80 cases of VAPP, and five cases of imported disease have been reported in the United States."
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"stopping oral polio vaccine use as soon as it is safely possible to do so"
Live virus vaccines spread disease.
"Within the past 4 years, poliomyelitis outbreaks associated with circulating vaccine-derived polioviruses (cVDPVs) have
occurred in Hispaniola (2000–01), the Philippines (2001), and Madagascar (2001–02). Retrospective studies have also detected
the circulation of endemic cVDPV in Egypt (1988–93) and the likely localized spread of oral poliovirus vaccine (OPV)-derived virus
in Belarus (1965–66). Gaps in OPV coverage and the previous eradication of the corresponding serotype of indigenous wild
poliovirus were the critical risk factors for all cVDPV outbreaks. The cVDPV outbreaks were stopped by mass immunization
campaigns using OPV. To increase sensitivity for detecting vaccine-derived polioviruses (VDPVs), in 2001 the Global Polio Laboratory
Network implemented additional testing requirements for all poliovirus isolates under investigation. This approach quickly led to
the recognition of the Philippines and Madagascar cVDPV outbreaks, but of no other current outbreaks. The potential risk of cVDPV
emergence has increased dramatically in recent years as wild poliovirus circulation has ceased in most of the world. The risk
appears highest for the type 2 OPV strain because of its greater tendency to spread to contacts. The emergence of cVDPVs
underscores the critical importance of eliminating the last pockets of wild poliovirus circulation, maintaining universally high
levels of polio vaccine coverage, stopping OPV use as soon as it is safely possible to do so, and continuing sensitive poliovirus
surveillance into the foreseeable future. Particular attention must be given to areas where the risks for wild poliovirus circulation
have been highest, and where the highest rates of polio vaccine coverage must be maintained to suppress cVDPV emergence."
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Polio in Nigeria Traced to Mutating Vaccine
Nigeria is fighting an unusual outbreak of polio caused by mutating polio vaccine, world health authorities say, but the only remedy is to keep vaccinating children there.
Officials of the World Health Organization fear that news of the outbreak will be a new setback for eradication efforts in northern Nigeria, where vaccinations were halted in 2003 for nearly a year because of rumors that the vaccine sterilized Muslim girls or contained the AIDS virus.
Officials deny suggestions that they kept the outbreak, which began last year, a secret, and say that they did not realize until recently that as many as 70 of Nigeria’s last 1,300 polio cases stemmed from a mutant vaccine virus rather than “wild type” virus, which causes most polio.
“It was an oversight on our part,” Dr. Bruce Aylward, director of the polio eradication campaign for the W.H.O., said yesterday. The agency discussed the first 16 cases it knew of at meetings early this year and posted information on its Web site in April, he said, “but only in places where lab people would look.”
Outbreaks of vaccine-derived polio are unusual but not unheard of. Individual cases have been known for years.
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Estimating the Extent of Vaccine-Derived Poliovirus Infection
Eight outbreaks of paralytic polio attributable to circulating vaccine-derived poliovirus (cVDPV) have highlighted the risks associated with oral poliovirus vaccine (OPV) use in areas of low vaccination coverage and poor hygiene. As the Polio Eradication Initiative enters its final stages, it is important to consider the extent to which these viruses spread under different conditions, so that appropriate strategies can be devised to prevent or respond to future cVDPV outbreaks.
This paper examines epidemiological (temporal, geographic, age, vaccine history, social group, ascertainment), and virological (type, genetic diversity, virulence) parameters in order to infer the numbers of individuals likely to have been infected in each of these cVDPV outbreaks, and in association with single acute flaccid paralysis (AFP) cases attributable to VDPVs. Although only 114 virologically-confirmed paralytic cases were identified in the eight cVDPV outbreaks, it is likely that a minimum of hundreds of thousands, and more likely several million individuals were infected during these events, and that many thousands more have been infected by VDPV lineages within outbreaks which have escaped detection.
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"the oral poliovirus vaccine (OPV) must eventually cease because of the risk of outbreaks of vaccine-derived polioviruses"
The final stages of the global eradication of poliomyelitis
The global incidence of poliomyelitis has dropped by more than 99 per cent since the governments of the world committed to eradication in 1988. One of the three serotypes of wild poliovirus has been eradicated and the remaining two serotypes are limited to just a small number of endemic regions. However, the Global Polio Eradication Initiative (GPEI) has faced a number of challenges in eradicating the last 1 per cent of wild-virus transmission. The polio endgame has also been complicated by the recognition that vaccination with the oral poliovirus vaccine (OPV) must eventually cease because of the risk of outbreaks of vaccine-derived polioviruses. I describe the major challenges to wild poliovirus eradication, focusing on the poor immunogenicity of OPV in lower-income countries, the inherent limitations to the sensitivity and specificity of surveillance, the international spread of poliovirus and resulting outbreaks, and the potential significance of waning intestinal immunity induced by OPV. I then focus on the challenges to eradicating all polioviruses, the problem of vaccine-derived polioviruses and the risk of wild-type or vaccine-derived poliovirus re-emergence after the cessation of oral vaccination. I document the role of research in the GPEI's response to these challenges and ultimately the feasibility of achieving a world without poliomyelitis.
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Understanding the recent polio outbreaks
Wild cases of polio are caused by poliovirus that is circulating naturally in the environment.
Vaccine-derived polioviruses are extremely rare and exist under specific circumstances. Oral polio vaccine contains live virus that is weakened so that it will prompt the body’s immune response without causing paralysis. The vaccine is ingested, and the weakened virus replicates in the child’s gut and is then excreted. In areas with poor sanitation, this excreted vaccine virus can spread to other children. This can actually be good because it then immunizes them. When the strain no longer finds susceptible children, it dies out.
The problem occurs in areas of low vaccination coverage. There, such vaccine-derived strains of the virus can continue to circulate as long as they continue to find unvaccinated or otherwise susceptible children. While they continue to circulate, they mutate. Eventually, if they are allowed to circulate long enough — at least 12 months — they can mutate into strains that are strong enough to cause paralysis.
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"As of 2017 vaccine-derived polio cases now outnumber those from the wild polio virus"
The tally for 2018 shows a dramatic swing: 98 cases of vaccine-derived polio; 29 cases of the wild version.
In 2018 they caused cases of paralytic polio in the Democratic Republic of Congo, Nigeria, Niger and Somalia. Genomic analysis of the strains involved showed that they had crossed borders, which is rare for vaccine-derived strains, and that some had circulated undetected for as long as four years.
In 2018 they caused cases of paralytic polio in the Democratic Republic of Congo, Nigeria, Niger and Somalia. Genomic analysis of the strains involved showed that they had crossed borders, which is rare for vaccine-derived strains, and that some had circulated undetected for as long as four years.
Health officials worry that the outbreaks may spread to neighbouring countries.
That is a setback for Africa. The last person on the continent paralysed by the wild polio virus was a Nigerian child who contracted the disease in 2016, so Africa has probably already eradicated the wild virus.
This leaves Afghanistan and Pakistan as its last two strongholds. But the outbreaks of vaccine-derived cases are a sign that polio's grand finale may be more drawn out than even pessimists expected. When wild polio virus disappears, the oral vaccine will be replaced with the injectable vaccine. How long such jabs will be needed to guard against the remnants of vaccine-derived polio is anybody's guess.
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what's troubling now is that there are currently more kids being paralyzed by cases of Polio from the vaccine than by the original "wild" variety.
"We have seen a lot more countries impacted this year than last year," says Dr. John Vertefeuille, the head of polio eradication at the U.S. Centers for Disease Control and Prevention.
There've been outbreaks this year in the Philippines, China, Myanmar, Pakistan and a half a dozen African countries.
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More Polio Cases Now Caused by Vaccine Than by Wild Virus
LONDON — Four African countries have reported new cases of polio linked to the oral vaccine, as global health numbers show there are now more children being paralyzed by viruses originating in vaccines than in the wild.
In a report late last week, the World Health Organization and partners noted nine new polio cases caused by the vaccine in Nigeria, Congo, Central African Republic and Angola. Seven countries elsewhere in Africa have similar outbreaks and cases have been reported in Asia. Of the two countries where polio remains endemic, Afghanistan and Pakistan, vaccine-linked cases have been identified in Pakistan.
In rare cases, the live virus in oral polio vaccine can mutate into a form capable of sparking new outbreaks. All the current vaccine-derived polio cases have been sparked by a Type 2 virus contained in the vaccine. Type 2 wild virus was eliminated years ago.
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WHO definition of a "vaccine derived virus" (vdv)
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Sixteen African nations are battling outbreaks of what's called "vaccine-derived polio." This is a form of polio that comes from the oral polio vaccine itself.
The oral vaccine contains a live but weakened version of the polio virus. The virus replicates inside the child's intestine and eventually is excreted. In places with poor sanitation, fecal matter can enter the drinking water supply, and the virus is able to start spreading from person to person. That was once considered a useful feature of the oral vaccine, since it can help unvaccinated children become immune. However, in rare cases in places with poor sanitation and large numbers of unvaccinated children, the attenuated virus can mutate in the wild and regain strength to the point where it can cause paralysis.
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