The re-emergence of polio: ‘Without full vaccination, the disease will not be eradicated’

“At one point, eradication of polio seemed within reach. Then the strict public health law reminded us: We must not slacken in our efforts,” says Mael Besod. This poliovirus specialist at the Pasteur Institute goes on to formulate the same instruction: “Let’s get vaccinated and stay vigilant. In Western countries, polio seems far away and nonexistent, but it still does.”

At the end of July, a case of polio appeared in the United States, the first in nearly a decade, as a booster shot. The affected man, a 20-year-old who resides in Rockland County, a suburb of New York, had gone to hospital with a paralysis of his leg. The diagnosis came quickly. He has not been vaccinated. Today, he is still partially paralyzed.

This highly contagious disease, caused by a virus that invades the nervous system and can cause permanent paralysis or even death, is nonetheless considered endemic in most parts of the planet. In 1988, there were about 350,000 cases per year, mostly in children under five, in 125 countries. Today, that number is down to 99%. Maël Bessaud welcomes “the amazing progress we owe to the massive vaccination campaigns launched by the Global Polio Eradication Initiative”. The virus continues to be endemic to only two countries: Afghanistan and Pakistan.

Vaccine vicious cycle

How do we explain that this American young man contracted a disease that was almost forgotten in Western countries? “Because as long as the virus is not 100% eradicated, it will continue to spread,” the specialist simply comments.

Possible first scenario: The patient went to a country where the virus is still circulating, or had contact with a patient who was returning from there. “Especially since the polio virus, which is transmitted by fecal-oral route through water, dirty food or a baby’s diaper, for example, has a peculiarity: it causes paralysis in only one patient out of about 200 patients,” explains Maël Bessaud. “This means that the number of people likely to carry it is much greater than the number of actual patients.” This is what happened recently in Malawi and Mozambique. Two children, who did not keep up with the vaccination, were infected with a strain of the virus from Pakistan, transmitted hidden by an asymptomatic person.

In the case of this American patient, genetic analyzes made it possible to exclude this pathway. This time, the explanation lies in the harmful effect of vaccination. Two types of vaccines have been disseminated worldwide: one, by injection, is most prevalent in developed countries; The other, orally, is used mainly everywhere else. “The first uses an inactivated vaccine,” explains Mael Besod. “It protects against disease but not from the virus. So you can be pregnant without knowing it and be dangerous if you come across someone who is not immune.”

He adds: “The oral vaccine is characterized by being easy to administer, but above all it protects against disease and prevents infection with the virus. Therefore, it is better to avoid human-to-human transmission.” “But in his case, we’re using the ‘attenuated’ polio virus, which is harmless but still alive.” In the weeks following vaccination, the patient will excrete this virus in their faeces and thus into the environment.

Nothing dangerous if everyone around him is vaccinated orally as well. “But if he’s in a community that hasn’t been vaccinated, or if he’s traveling to an area where only the injection vaccine is used, the virus may start spreading again.” And this is where the problem can arise: if it spreads for several months, it can, through mutations, become malignant again. “This is what happened to this American patient. He was exposed to this viral strain derived from an oral vaccine, and he developed symptoms because he was not vaccinated,” summarizes Mile Pisaud.

Worldwide, 698 cases of polio related to derivatives of vaccine strains were detected worldwide in 2021, according to the World Health Organization, in unvaccinated people alone.

Virus spreads in stealth mode

The polio virus expert insists again that “this patient comes to remind us that even if we feel protected, the virus is still there and the only way to protect ourselves from it is to receive a vaccination.” Proof of this, in mid-August, the US Centers for Disease Control and Prevention (CDC) announced that the strain of poliovirus that infected the young man had been detected in several samples of sewage taken between May and July. Where is Rockland, near Orange and New York.

And the United States is not alone involved. In the UK, the warning was issued as early as June. Traces of the polio virus were found in sewage from eight London boroughs. “The analyzes show that these collected strains are related to those found in the United States, as well as to other strains taken in Jerusalem,” Mael Pisod notes. “The virus not only spreads well, it crosses borders.” In response, the United Kingdom, where unlike France vaccination against polio is not mandatory, introduced an injection to all London children aged 1-9 years.

“For the majority of the population, who have been vaccinated, there is little risk. But this increases once we enter neighborhoods or within communities where the vaccination rate is low,” the specialist notes. “It also demonstrates the importance of keeping up with augmented shots.” In France, the first injection is done after two months, then after four and eleven months. It is then necessary to implement reminders after 25, 45, 65 years and then every ten years.

Mile Pesaud’s concern is growing that the Covid-19 crisis has led to the largest drop in childhood vaccinations in nearly thirty years, according to the United Nations. 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, about 25 million children missed a single dose. Or more doses of the polio vaccine in 2021.

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Hope for a new vaccine

Will we ever succeed in eradicating polio completely from the entire planet? “Unfortunately, I am afraid that we have reached the vaccination ceiling,” the specialist from the Pasteur Institute laments. “Some areas of the world are difficult to access for security reasons, especially in Africa. In other areas, especially in Pakistan and Afghanistan, we are facing populations that categorically refuse to vaccinate their children,” he elaborated. “Without full vaccination, the disease will not be eradicated.”

Despite everything, the specialist wants to be an optimist. “The virus in its wild form is regressing. In 2021, only six cases have been identified,” he says. A new oral vaccine is currently being tested, which would reduce the risk of the virus becoming pathogenic again. It concludes, “It’s currently being run in about two dozen countries. And in a year or two we’ll see if it works.” “And then we can hope to deal with zero cases.”