By MARIA CHENG, AP Medical Editor
LONDON (AP) — For years, global health officials have used billions of drops of an oral vaccine in a remarkably effective campaign to wipe out polio in its last remaining strongholds — typically impoverished and politically unstable corners of the world. world.
Now, in a surprising twist to 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 known about this extremely rare phenomenon for a long time. This is why some countries have switched to other polio vaccines. But these accidental oral infections are becoming more blatant as the world moves closer to eradicating the disease and the number of polio cases caused by wild or naturally circulating virus plummets.
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Since 2017, there have been 396 cases of polio caused by the wild virus, compared to 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 virus in the vaccine, which is now leading to new outbreaks,” said Scott Barrett, a Columbia University professor who has studied polio eradication. “I suspect countries like the UK and the US will be able to stop transmission fairly quickly, but we’ve thought about that about monkeypox as well.”
The latest incidents represent the first time in several years that the vaccine-related polio virus has appeared in wealthy countries.
Earlier this year, Israeli officials detected polio in an unvaccinated 3-year-old child who suffered from paralysis. Several other children, almost all unvaccinated, were found to be carriers of the virus but without any symptoms.
In June, British authorities reported finding evidence in sewage that the virus was spreading, although no infections in people were identified. Last week the government said all children in London aged 1 to 9 would be offered a booster shot.
In the United States, an unvaccinated young adult suffered paralysis of his legs after being infected with polio, officials in New York revealed last month. The virus has also appeared in sewers in New York, suggesting it is spreading. But officials said they weren’t planning a booster campaign because they believed the state’s high vaccination rate should provide enough protection.
Genetic analyzes showed that the viruses in the three countries were all “vaccine-derived”, meaning they were mutated versions of a virus from the oral vaccine.
The oral vaccine in question has been used since 1988 because it’s cheap, easy to administer – two drops are 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.
But it can also cause poliomyelitis in about two to four children for 2 million doses. (Four doses are needed to be fully immunized.) In extremely rare cases, the weakened virus can also sometimes mutate into a more dangerous form and trigger outbreaks, especially in places with poor sanitation and vaccination levels. weak.
These outbreaks usually begin when vaccinated people shed live vaccine virus in their stool. From there, the virus can spread within the community and, over time, morph into a form that can cripple people and trigger new outbreaks.
Many countries that have eliminated polio have switched to injectable vaccines containing virus killed decades ago to avoid such risks; the Nordic countries and the Netherlands have never used the oral vaccine. The ultimate goal is to switch the world to vaccines once wild polio is eradicated, but some scientists say the switch should happen sooner.
“We probably never could have brought polio under control in the developing world without the (oral polio vaccine), but that’s the price we’re paying now,” said Dr Paul Offit, director of the Vaccine Education Center at the Children’s Philadelphia Hospital. “The only way to eliminate poliomyelitis is to eliminate 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 major surprise”, saying officials were focused on eradication of the disease in Afghanistan and Pakistan, where health workers have been killed. for the vaccination of children and where the conflict has made access to certain areas impossible.
Still, O’Leary said he was confident that Israel, Britain and the United States would quickly stop their newly identified outbreaks.
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 approximately 350,000 cases of wild poliomyelitis 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 vaccine-related polio cases peaked at more than 1,100 spread across dozens of countries. It has since declined to around 200 this year so far.
Last year, WHO and partners also began using a new 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, what is needed is more vaccination, experts say. That’s something Barrett of Columbia University worries might be difficult in the age of COVID-19.
“What’s different now is a reduction in trust in authority and political polarization in countries like the US and the UK,” Barrett said. “The presumption that we can rapidly increase the number of vaccinations may be more difficult now.”
Oyewale Tomori, a virologist who helped lead Nigeria’s efforts to eliminate polio, said that in the past he and his colleagues were hesitant to describe outbreaks as ‘vaccine-derived’, fearing people would fear the vaccine. .
“All we can do is explain how the vaccine works and hope people understand that vaccination is the best protection, but it’s complicated,” Tomori said. “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.”
The Associated Press Health and Science Department is supported by the Howard Hughes Medical Institute Department of Science Education. The AP is solely responsible for all content.
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