For years, global health officials have used billions of drops of an oral vaccine in a remarkably effective campaign aimed at wiping out polio in its last remaining strongholds — typically, poor, politically unstable corners of the world. Now, in an unexpected twist to the long-running effort to eliminate the virus, officials in New York, London and Jerusalem have found evidence of polio spreading in those areas.
The original source of the virus? The oral vaccine itself.
Scientists have long known about this extremely rare phenomenon. That is why some countries have switched to other polio vaccines. These accidental infections caused by oral vaccines are more common as we move closer to eliminating the disease.
Since 2017, there have been 396 cases of polio caused by the wild virus, versus more than 2,600 linked to the oral vaccine, according to figures from the World Health Organization and its partners. We are basically replacing wild virus with vaccine virus, which leads to new outbreaks,” Scott Barrett of Columbia University, who is a professor in polio elimination. “I would assume that countries like the U.K. and the U.S. will be able to stop transmission quite quickly, but we also thought that about monkeypox.”
The latest incidents represent the first time in several years that vaccine-connected poliovirus has turned up in rich countries.
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.
In June, British officials reported that they found evidence of the virus in sewage, but no cases were confirmed. Last week, the government said all children in London ages 1 to 9 would be offered a booster shot.
In the U.S., an unvaccinated young adult suffered paralysis in his legs after being infected with polio, New York officials revealed last month. It has been shown up in New York’s sewers , suggesting that it is spreading. But officials said they are not planning a booster campaign because they believe the state’s high vaccination rate should offer enough protection.
Genetic analysis showed that all three viruses were “vaccine-derived”, meaning they were modified versions of the same virus found in oral vaccines.
The oral vaccine at issue has been used since 1988 because it is cheap, easy to administer — two drops are put directly into children’s mouths — and better at protecting entire populations where polio is spreading. This vaccine contains the live virus in a weaker form.
But it can also cause polio in about two to four children per 2 million doses. Four doses of the vaccine are needed to ensure that you’re fully immunized. In extremely rare cases, the weakened virus can also sometimes mutate into a more dangerous form and spark outbreaks, especially in places with poor sanitation and low vaccination levels.
These outbreaks typically begin when people who are vaccinated shed live virus from the vaccine in their feces. The virus spreads within communities and can become a deadly disease that could paralyze and infect others.
Many countries who eliminated polio switched from oral to injectable vaccines decades ago. The Netherlands and Nordic countries have never used an oral vaccine. Although the ultimate goal of polio elimination is for the whole world to be vaccinated, some experts believe that it should occur sooner.
” Without the (oral polio vaccine), we probably wouldn’t have been able to get on top of polio among the developing world, but that’s the price we’re currently paying,” Dr. Paul Offit of the Vaccine Education Center of Philadelphia said. “The only way we are going to eliminate polio is to eliminate the use of the oral vaccine.”
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. O’Leary stated that he believes Israel, Britain, and the U.S. would quickly eliminate their new outbreaks.
The oral vaccine has been credited for dramatically decreasing the number of children paralyzed from 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.
In 2020, the number of polio cases linked to the vaccine hit a peak of more than 1,100 spread out across dozens of countries. It has since declined to around 200 this year so far.
In the last year, WHO and its partners began to use a more recent oral polio vaccine. This new vaccine contains a weakened, but still active virus, scientists think is less likely than a deadly form. But supplies are limited.
Experts say more vaccines are needed to stop poliomyelitis in Britain, Israel and the U.S. That is something Columbia University’s Barrett worries could be challenging in the COVID-19 era.
“What is different is the reduction in trust in authorities and political polarization countries such as the U.S., Barrett stated. “The presumption that we can quickly get vaccination numbers up quickly may be more challenging now.”
Oyewale Tomori, a virologist who helped direct Nigeria’s effort to eliminate polio, said that in the past, he and colleagues balked at describing outbreaks as “vaccine-derived,” wary it would make people fearful of the vaccine.
“We can only explain the vaccine and make people aware that it is the best way to protect themselves. But, that’s a complicated process.” Tomori stated. “In hindsight, maybe it would have been better not to use this vaccine, but at that time, nobody knew it would turn out like this.”
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