Resurgence of polio: “Without full vaccination, the disease will never be eradicated”

Resurgence of polio: "Without full vaccination, the disease will never be eradicated"

The discovery of a case of polio in the United States and traces of the virus in wastewater from the United Kingdom and Israel raise fears of a resurgence of this disease declared eradicated in much of the planet. A reminder of the importance of vaccination in the fight against polio, for which there is no cure.

“At one point, polio eradication seemed within reach. Then the harsh public health law reminded us: we must never give up our efforts,” says Maël Bessaud. This poliovirus specialist from the Institut Pasteur continues to give the same instruction: “Let’s get vaccinated and stay alert. In Western countries, polio seems distant, nonexistent, but it’s still there.”

At the end of July, a case of polio appeared in the United States as a booster vaccine, the first in almost ten years. The affected, 20-year-old resident of Rockland County, a suburb of New York, had gone to the hospital because of paralysis in the leg. The diagnosis came quickly. He was not vaccinated. Today, he still suffers from partial paralysis.

This highly contagious disease, caused by a virus that invades the nervous system and can cause permanent paralysis or even death, is nevertheless considered eradicated in most of the planet. In 1988, there were about 350,000 cases per year, most in children under five years of age, in 125 countries. Today, that number has dropped to 99%. “Incredible progress that we owe to the mass vaccination campaigns launched by the Global Polio Eradication Initiative”, greets Maël Bessaud. The virus continues to circulate endemically in only two countries: Afghanistan and Pakistan.

A vicious cycle of vaccinations

So how to explain that this young American contracted a disease almost forgotten in Western countries? “Because as long as it is not 100% eradicated, the virus will continue to circulate,” the specialist limits himself to commenting.

First possible scenario: the patient went to a country where the virus is still circulating, or was in contact with a patient returning from there. “Especially because the poliovirus, which is transmitted fecal-oral through water, dirty food or a child’s diaper, for example, has a specificity: it only causes paralysis in one patient out of about 200”, explains Maël Bessaud. “This means that the number of people likely to carry it is much higher than the number of actual patients.” This is what happened recently in Malawi and Mozambique. Two children, not up to date on their vaccinations, were infected with a strain of the virus from Pakistan, transmitted occultly through an asymptomatic person.

However, in the case of this American patient, genetic analyzes have ruled out this clue. This time, the explanation lies in a pernicious effect of vaccination. Two types of vaccines have been deployed throughout the world: one, by injection, is the most widespread in developed countries; the other, oral, is used mostly everywhere. “The first uses an inactivated vaccine”, explains Maël Bessaud. “It protects against the disease but not against the virus. Therefore, you can be a carrier without knowing it and be a danger if you meet an unvaccinated person.”

“The oral vaccine has the advantage of being easy to administer, but above all it protects from the disease and avoids contamination by the virus, so it is better to avoid person-to-person transmission,” he continues. “But in his case, we are using a ‘attenuated’ poliovirus, which is harmless but still alive.” In the weeks following vaccination, the patient will excrete this virus in their faeces and thus in the environment.

Nothing serious if everyone around you is also vaccinated orally. “But if you’re in a community that isn’t vaccinated, or if you travel to an area where only the injectable vaccine is used, the virus can start circulating again.” And this is where the problem can arise: if it spreads over several months, it can, by mutations, become virulent again. “This is what happened to this American patient. He was exposed to this strain of the virus derived from an oral vaccine, and developed symptoms because he was not vaccinated”, summarizes Maël Bessaud.

Worldwide, 698 polio cases linked to derivatives of vaccine strains were detected worldwide in 2021, according to the WHO, in unvaccinated people alone.

A virus that circulates incognito

“This patient therefore comes to remind us that although we feel protected, the virus is still there and the only way to protect ourselves is to get vaccinated,” the poliovirus expert insists again. Proof of this is that, in mid-August, the United States Centers for Disease Control and Prevention (CDC) announced that the strain of poliovirus that infected the young man had been detected in several wastewater samples taken between May and July in Rockland County where he is from, in neighboring Orange and in New York.

And the United States is not the only one affected. In the United Kingdom, the alert was given as early as June. Traces of poliovirus have been found in sewage from eight London boroughs. “And the analyzes show that these collected strains are linked to those found in the United States, and also to others taken in Jerusalem,” says Maël Bessaud. “The virus is not only circulating well, but it is crossing borders.” In response, the UK, where polio vaccination is not compulsory unlike France, offered every child in London aged 1-9 a shot.

“For the majority of the population, vaccinated, there is little risk. But this increases as soon as we enter neighborhoods or within communities where the vaccination rate is low, “says the specialist. “It also shows the importance of keeping up with booster shots.” In France, the first injection is done at two months, then at four and eleven months. Then it is necessary to carry out reminders at 25, 45, 65 years and then every ten years.

The concern is even more acute, for Maël Bessaud, that the Covid-19 crisis has caused the greatest decrease in childhood vaccination in almost thirty years, according to the UN. According to a report published in July, the proportion of children who received all three doses of the diphtheria, tetanus, and polio (DTP) vaccine fell from 86% in 2019 to 81% in 2021. In all, some 25 million children did not receive one or more doses of polio vaccine in 2021.

>> Read also: “Measles vaccination in France, a collateral victim of Covid-19”

Hope for a new vaccine

Will we one day be able to completely eradicate polio from the entire planet? “Unfortunately, I fear that we are reaching a ceiling in vaccination,” laments the specialist from the Institut Pasteur. “Certain zones in the world are difficult to deal with for security reasons, notably in Africa. Dans d’autres, notamment au Pakistan et en Afghanistan, are confronted with a population that refuses catégoriquement de vaccinating leurs enfants”, detailed-t -The. “And without full vaccination, the disease will never be eradicated.”

Despite everything, the specialist wants to be optimistic. “The virus in its wild form is losing ground. In 2021, only six cases have been identified,” he says. And a new oral vaccine is currently being tested, which should limit the risk of the virus becoming pathogenic again. “Currently it is administered in twenty countries. In one or two years we will see if it works”, he concludes. “And then we can expect to get closer to zero cases.”

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