Polio spread in Israel, US, UK highlights extremely rare risk of oral vaccine

LONDON (AP) – Over the years, global health officials have used billions of drops of oral vaccine in a remarkably effective campaign aimed at eradicating polio in their last remaining strongholds – usually, the world’s poor, politically unstable in the corners.

Now, in a surprise twist in a decades-long effort to eradicate the virus, officials in Jerusalem, New York and London have discovered evidence that polio is spreading there.

Original source of virus? Oral vaccine only.

Scientists have known about this extremely rare phenomenon for a long time. This is why some countries have turned to other polio vaccines. But these accidental infections from oral formula are becoming more apparent as the world nears eradication of the disease, and the number of polio cases caused by wild or naturally transmitted viruses is declining.

Since 2017, 396 cases of polio have been caused by the wild virus, according to data from the World Health Organization and its partners, while more than 2,600 have been linked to oral vaccines.

“We are basically replacing the wild virus in the vaccine with the virus, which is now leading to new outbreaks,” said Scott Barrett, a Columbia University professor who studied polio eradication. “I think countries like the UK and the US will be able to stop transmission very quickly, but we thought about monkeypox as well.”

The latest developments mark the first time in many years that vaccine-associated poliovirus has emerged in wealthy countries.

Earlier this year, authorities in Israel detected polio in a 3-year-old illiterate child who was paralyzed. Several other children, almost all of whom had not been vaccinated, were found to have the virus but had no symptoms.

In June, British officials reported finding evidence in sewage that the virus was spreading, although no infections were identified in people. Last week, the government said a booster shot would be given to all children aged 1 to 9 in London.

New York officials revealed last month that in the US, an illiterate young adult was paralyzed in his legs after being infected with polio. The virus has also appeared in the sewers of New York, indicating that it is spreading. But officials said they are not planning a booster campaign because they believe the state’s high vaccination rate should provide enough protection.

Genetic analysis showed that the viruses in all three countries were “vaccine-derived”, meaning they were mutated versions of a virus that originated in an oral vaccine.

The controversial oral vaccine has been in use since 1988 because it is cheaper, easier to administer – two drops put directly into children’s mouths – and is better at protecting entire populations where polio is spreading. It contains a weakened form of a live virus.

But it can also cause polio in about two to four children per 2 million doses. (Four doses are required to be fully immunized.) In extremely rare cases, the weakened virus can sometimes mutate into a more dangerous form and spark outbreaks, especially with poor hygiene and low vaccination levels. in the places.

Polio vaccination site in Maiduguri, Nigeria in 2016. (AP photo/Sunday Alamba, file)

These outbreaks usually begin when vaccinated people shed live virus from the vaccine in their feces. From there, the virus can spread within the community and, over time, mutate into a form that can paralyze people and start new epidemics.

To avoid such risks, many countries introduced vaccines containing a killed virus to injectable vaccines that eradicated polio decades ago; The Nordic countries and the Netherlands never used oral vaccines. The ultimate goal is to get the whole world in the shots once wild polio is eradicated, but some scientists argue the switch should happen soon.

“We probably wouldn’t have gotten on top of polio 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 Children’s Vaccine Education Center. Hospital of Philadelphia. “The only way to eliminate polio is to eliminate the use of oral vaccines.”

Aidan O’Leary, director of the WHO’s polio department, described the discovery of polio outbreaks in London and New York as “a big surprise”, saying officials are focused on eradicating the disease in Afghanistan and Pakistan, where health workers have died. . and where conflict has made access impossible in some areas to vaccinate children.

Still, O’Leary said he was confident that Israel, Britain and the US would close their newly identified outbreaks quickly.

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, 19 cases of wild polio have been reported in Pakistan, Afghanistan and Mozambique.

In 2020, the number of vaccine-associated polio cases reached a peak of more than 1,100 spread across dozens of countries. So far this year it has come down to around 200.

Then-President Shimon Peres watches as a medical worker administers a dose of polio vaccine to a young boy at a clinic in Jerusalem on August 21, 2013. (Flash90)

Last year, the WHO and partners began using a new oral polio vaccine, which contains a live but weakened virus that scientists believe is less likely to turn into a dangerous form. But the supply is limited.

Experts say more vaccinations are needed to prevent polio in the UK, US and Israel. This is something that Columbia University’s Barrett concerns may be challenging in the COVID-19 era.

“What’s different now is the lack of trust in the authorities and political polarization in countries like the US and the UK,” Barrett said. “Estimates that we can get vaccination numbers quickly now may be more challenging.”

Oyewale Tomori, a virologist who helped direct Nigeria’s efforts to eliminate polio, said that, in the past, he and his colleagues have described outbreaks as “vaccine-derived”. Had avoided doing it, people would be scared of the vaccine.

“We can only explain how the vaccine works and hope that people understand that vaccination is the best protection, but it is complicated,” Tomori said. “Ultimately, maybe it would have been better not to use this vaccine, but at the time no one knew it would turn out that way.”