Doctors found that a British man has been excreting live polio virus for nearly 28 years, despite being vaccinated. These sort of cases aren't unique, but this is by far the longest cases seen thus far. Moreover, the immune deficiency has allowed the virus to mutate and replicate inside the man's body. Doctors say, however, that there are no health hazards involved since the man lives in a immunized community. It's important to mention that the vaccine in question was the oral polio vaccine which has been discontinued for some time.
Polio can cause fever, pain, vomiting and, in rare cases, permanent paralysis, which is why the man in question needs to take special proteins that keeps the virus living inside him in check.
Until two decades ago, the oral poliovirus vaccine used to be the norm. Since it was licensed in the United States in 1962 immunization with these vaccines lead to the eradication of poliomyelitis in this country. Sometimes, though, the live-attenuated oral poliovaccine (OPV) can cause poliomyelitis (0,0000005% of the time). The vaccine is basically made up of a live, attenuated (weakened) vaccine-virus. When a child receives OPV - once they got other polio shots - the weakened vaccine-virus replicates in the intestine and enters into the bloodstream, triggering a protective immune response in the child. Like wild poliovirus, the child excretes the vaccine-virus for a period of six to eight weeks. Sometimes, the virus the child excretes isn't the same as the virus from the vaccine, so you end up with a new virus which can be possibly hazardous to a community. On very rare occasions, if a population is seriously under-immunized, there are enough susceptible children for the excreted vaccine-derived polioviruses to begin circulating in the community. These viruses are called circulating vaccine-derived polioviruses (cVDPV).
"There are currently huge efforts by the World Health Organization and partners to complete global polio eradication. With the significant decline in poliomyelitis cases due to wild poliovirus in recent years, rare cases related to the use of live-attenuated oral polio vaccine assume greater importance. Poliovirus strains in the oral vaccine are known to quickly revert to neurovirulent phenotype following replication in humans after immunisation. These strains can transmit from person to person leading to poliomyelitis outbreaks and can replicate for long periods of time in immunodeficient individuals leading to paralysis or chronic infection, with currently no effective treatment to stop excretion from these patients."
Luckily, polio vaccine today are good at battling most strains, while OPV has been discontinued in the US and UK in 200 and in 2005, respectively. The man in question, though, got his OPV dose in 1986, and has been excreting the live polio virus for 28 years now.
Nothing comes close to this particular case which Olen Kew of the Centers for Disease Control and Prevention in Atlanta calls a "record holder". The researchers at National Institute for Biological Standards and Control in Potters Bar, England who studied the case found the man excreted several strains which contained changes to surface regions that human immune proteins attack. All of these strains are, however, controlled by current vaccines. There's no danger, but the situation needs to be followed up closely since there's always the risk that some day a special case like this might lead to a new polio virus strain which vaccines today can't fight.
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While the case described in PLOS Pathogens is a rarity, three could be more vaccinated people who excrete live viruses than thought. Live viruses turned up in sewage from Israel, Finland, Slovakia and Estonia. There aren't any problems because these countries are 99% immunized. To get an idea, in 2009 50% of the world's poliomyelitis were reported in India - today there are none.