For years, health officials around the world have used billions of drops of an oral vaccine in a remarkably successful campaign to eradicate polio in the last remaining strongholds, often poor and politically unstable corners of the world. world.
Now, in a stunning twist in the decades-long effort to eradicate the virus, authorities in Jerusalem, New York and London have uncovered evidence that polio is spreading there.
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. But these incidental infections from oral formula are becoming more noticeable as the world moves ever closer to eradicating the disease and the number of polio cases caused by the wild or naturally circulating virus plummets. .
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’re basically replacing the wild virus with the vaccine virus, which is now causing new outbreaks,” said Scott Barrett, a Columbia University professor who has studied polio eradication. “I guess countries like the UK and the US will be able to stop transmission pretty quickly, but we think that about monkeypox as well.”
The latest incidents represent the first time in several years that the vaccine-related polio virus has turned up in rich countries.
Earlier this year, officials in Israel detected polio in an unvaccinated three-year-old boy who suffered from paralysis. Several other children, almost all unvaccinated, were found to have the virus but no symptoms.
In June, British authorities reported finding evidence in sewage that the virus was spreading, although no infections were identified in people. Last week, the government said all London children aged one to nine would be offered a booster shot.
In the US, an unvaccinated young adult suffered paralysis in his legs after being infected with polio, New York officials revealed last month. The virus has also appeared in the sewers of New York, suggesting that it is spreading. But officials said they aren’t planning a booster campaign because they believe the state’s high vaccination rate should offer enough protection.
Genetic analyzes showed that the viruses in the three countries were all “vaccine-derived,” meaning they were mutated versions of a virus that originated in the oral vaccine.
The oral vaccine in question has been used since 1988 because it is inexpensive, easy to administer (two drops are placed directly in the mouth of children), and better protects entire populations where polio is spreading. It contains a weakened form of the live virus.
But it can also cause polio in about two to four children for every 2 million doses. (Four doses are required to be fully immunized.) In extremely rare cases, the weakened virus can also mutate into a more dangerous form and cause outbreaks, especially in places with poor sanitation and low levels of vaccination.
These outbreaks usually start when vaccinated people shed live vaccine virus in their feces. From there, the virus can spread within the community, eventually turning into a form that can cripple people and start new epidemics.
Many countries that eliminated polio switched to injectable vaccines containing a virus killed decades ago to avoid such risks; the Nordic countries and the Netherlands never used the oral vaccine. The ultimate goal is to get everyone injecting once wild polio is eradicated, but some scientists argue the change should happen sooner.
“We probably never would have been able to beat polio in the developing world without the (oral polio vaccine), but this is the price we’re paying now,” said Dr. Paul Offit, director of the Children’s Vaccine Education Center. Philadelphia Hospital. “The only way we are going to eliminate polio is by eliminating the use of the oral vaccine.”
Aidan O’Leary, director of the WHO’s polio department, described the discovery of the spread of polio in London and New York as “a huge surprise”, saying officials have been focused on eradicating the disease in Afghanistan and Pakistan, where health workers have been killed. to immunize children and where conflict has made access to some areas impossible.
Still, O’Leary said he is confident Israel, Britain and the United States will quickly shut down their newly identified outbreaks.
The oral vaccine is credited with drastically 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 each year. So far this year, there have been 19 cases of wild polio, all in Pakistan, Afghanistan and Mozambique.
In 2020, the number of vaccine-related polio cases reached a peak of more than 1,100 spread across dozens of countries. Since then, it has dropped to around 200 this year so far.
Last year, the WHO and its partners also began using a newer oral polio vaccine, which contains a live but weakened virus that scientists say is less likely to mutate into a dangerous form. But supplies are limited.
To stop polio in Britain, the United States and Israel, more vaccination is needed, experts say. That’s something Columbia University’s Barrett worries could be a challenge in the age of COVID-19.
“What is different now is a reduction in trust in authorities and political polarization in countries like the United States and the United Kingdom,” Barrett said. “The assumption that we can rapidly increase vaccination numbers may be more challenging now.”
Oyewale Tomori, a virologist who helped lead Nigeria’s efforts to eliminate polio, said that in the past, he and his colleagues were reluctant to describe outbreaks as “vaccine-related,” fearing that people would fear the vaccine.
“All we can do is explain how the vaccine works and hope that people understand that immunization is the best protection, but it’s complicated,” Tomori said. “In retrospect, it might have been better not to use this vaccine, but at the time, no one knew it would turn out that way.”
The Associated Press Health and Science Department receives support from the Howard Hughes Medical Institute’s Department of Science Education. The AP is solely responsible for all content.
Maria Cheng, The Associated Press
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