The oral vaccine at issue has been used since 1988 because it's cheap, easy to administer — two drops put directly into children's mouths — and better at protecting entire populations where polio is spreading. It contains a weakened form of the live virus.
Earlier this year, officials in Israel detected polio in an unvaccinated 3-year-old, who suffered paralysis. Several other children, nearly all of them unvaccinated, were found to have the virus but no symptoms.
Genetic analyses showed that the viruses in the three countries were all “vaccine-derived,” meaning that they were mutated versions of a virus that originated in the oral vaccine. These outbreaks typically begin when people who are vaccinated shed live virus from the vaccine in their feces. From there, the virus can spread within the community and, over time, turn into a form that can paralyze people and start new epidemics.
Aidan O’Leary, director of WHO's polio department, described the discovery of polio spreading in London and New York as “a major surprise,” saying that officials have been focused on eradicating the disease in Afghanistan and Pakistan, where health workers have been killed for immunizing children and where conflict has made access to some areas impossible.
The oral vaccine is credited with dramatically reducing the number of children paralyzed by polio. When the global eradication effort began in 1988, there were about 350,000 cases of wild polio a year. So far this year, there have been 19 cases of wild polio, all in Pakistan, Afghanistan and Mozambique.
To stop polio in Britain, the U.S. and Israel, what is needed is more vaccination, experts say. That is something Columbia University's Barrett worries could be challenging in the COVID-19 era.
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