Polio in UK, US and elsewhere reveals rare risk of oral vaccine

Over the years, global health authorities have launched highly effective campaigns aimed at eradicating polio in its last remaining strongholds, usually in poor and politically unstable parts of the world. It has used billions of drops of oral vaccine in campaigns.

Now, in a surprising twist to decades of efforts to eradicate the virus, authorities in London, New York and elsewhere have found evidence that polio is spreading there.

Where did the virus come from? Oral vaccine itself.

Scientists have long known about this extremely rare phenomenon. As a result, some countries have switched to other polio vaccines. But as the world moves closer to eradicating the disease and the number of polio cases caused by wild or naturally circulating viruses plummets, these accidental infections from oral prescriptions are becoming increasingly prominent.

Statistics from the World Health Organization and its partners show that since 2017, there have been 396 cases of polio caused by wild-type viruses and more than 2,600 cases associated with oral vaccines.

Scott Barrett, a professor at Columbia University who studies polio eradication, said, “We’re basically replacing the virus in the wild with the virus in vaccines, which is now leading to new outbreaks.” I think countries like the UK and the US can stop the epidemic very quickly, and that’s what I thought about monkeypox.”

The latest case represents the first outbreak in years of a vaccine-related poliovirus in a rich country.

Earlier this year, Israeli officials discovered that an unvaccinated 3-year-old child who had been paralyzed had contracted polio. Several other children, nearly all unvaccinated, were found to have the virus but had no symptoms.

In June, British authorities reported finding evidence of the virus spreading through sewage, but no human transmission was confirmed. Announced to give booster shots to children.

In the United States, an unvaccinated young adult was left with paralyzed legs after contracting polio, officials in New York said last month. suggests. But officials said they were not planning a booster campaign because they believed the state’s high vaccination rates should provide adequate protection.

Genetic analysis showed that the viruses in all three countries were ‘vaccine-derived’. In short, these viruses were mutated versions of viruses derived from oral vaccines.

The oral vaccine in question has been in use since 1988. Because it’s cheap, easy to administer (two drops can be put directly in a child’s mouth), and great for protecting entire polio-endemic areas. Contains live, attenuated virus.

But two million doses can also cause polio in about two to four children. (He needs four doses to be fully immune.) In very rare cases, a weakened virus mutates into a more dangerous form, especially when sanitation is poor and vaccination levels are low. It can also cause outbreaks at low altitudes.

These outbreaks usually begin when vaccinated people shed live vaccine-derived virus in their faeces. From there, the virus spreads within the community and, over time, can morph into forms that paralyze people and start new epidemics.

Many polio-free countries have switched to injectable vaccines containing the decades-old dead virus to avoid such risks. Nordic countries and the Netherlands have never used oral vaccines. The ultimate goal is to transition the whole world to vaccination once wild polio is eradicated, but some scientists argue that the switch should come sooner.

“Without (oral polio vaccine), we would never have beaten polio in developing countries, but this is the price we are paying now,” said Paul, director of the Children’s Center for Vaccine Education. Dr. Offitt said. Philadelphia hospital. “The only way to eradicate polio is to stop using the oral vaccine.”

Aidan O’Leary, director of the WHO’s polio division, described the discovery of polio epidemics in London and New York as a “huge surprise” and said authorities are determined to eradicate the disease in Afghanistan and Pakistan, where health workers have died. Vaccination of children and places where conflict has made some areas inaccessible.

Still, O’Leary said he was confident Israel, the UK and the US would quickly contain the newly confirmed outbreak.

Oral vaccines have been 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 polio annually. So far this year, he has had 19 cases of wild polio in Afghanistan, Mozambique and Pakistan.

In 2020, the number of vaccine-related polio cases peaked at over 1,100 spread across dozens of countries. Since then, it has dropped to about 200 so far this year.

Last year, WHO and its partners also launched a new oral polio vaccine. The vaccine contains live but weakened viruses that scientists believe are unlikely to mutate into dangerous forms, but supplies are limited.

Experts say more vaccinations are needed to eradicate polio in Britain, Israel and the United States. This is what Columbia University’s Barrett is concerned about, and could be difficult in the time of COVID-19.

“The difference now is the declining trust in authorities and political polarization in countries like the US and the UK,” Barrett said. “The assumption that the number of vaccinations can be increased soon may be more difficult now.”

Oyewale Tomori, a virologist who helped lead Nigeria’s polio eradication effort, said in the past that he and colleagues were hesitant to describe outbreaks as “vaccine-derived,” fearing that people would become afraid of vaccines. said he was concerned.

“All we can do is explain how vaccines work and convince people that vaccination is their best defense, but it’s complicated.” It may have been better not to use this vaccine, but at the time no one expected this outcome.”