London, Israel, New York State… For the first time in years, polio has returned to various parts of the world. In June, the virus was detected in sewage in the English capital, forcing British authorities to step up vaccinations for children in London on Wednesday.

Poliomyelitis, which primarily affects children, is a highly contagious disease that invades the nervous system and can cause permanent paralysis. In the most serious cases, it can even lead to death.

The fight against the virus has intensified in recent decades, and with an incidence rate that has been reduced by 99% since 1988, the disease is “on the verge of being eradicated on a global scale”, underlines the WHO. In 2021, only six cases were reported, compared to an estimated 350,000 cases 30 years ago.

“Reassuring” vaccine coverage

But the resurgence of the virus worries authorities around the world, especially since there is no treatment for polio. “The main preventive measures are related to hygiene and vaccination,” indicates Public Health France.

In a bulletin published in early summer, the health agency explains that “the excellent” vaccination coverage in France “is reassuring.” In 2019, the primary vaccination rate was 99% and 96% for the booster in infants. Since 2018, polio vaccination is mandatory.

“It provides very good protection against the disease in the event of contamination, so the risk of the appearance of cases and/or clusters in the French population remains very low,” summarizes SPF.

Many asymptomatic cases

However, the appearance of cases in France is not impossible. “We are not immune,” he affirms with our colleagues from the Parisian researcher Maël Bessaud, specialist on the subject at the Institut Pasteur.

Especially since, according to the World Health Organization, “up to 90% of infected subjects remain asymptomatic or show mild symptoms. So the disease usually goes unnoticed.” It is mainly transmitted through contaminated water, aerosols or food contaminated by feces.

“Infected people can transmit the infection as long as the virus persists in the throat (one week) and in the feces (three to six weeks or even longer),” warns the Institut Pasteur.

Catch-up vaccination in unvaccinated population groups is therefore very important to prevent the occurrence of clusters.

Except that, globally, the proportion of children who received all three doses of the diphtheria, tetanus, and polio (DTP) vaccine fell from 86% in 2019 to just 81% in 2021. “This is a red flag.” red for the health of children,” warns Catherine Russel, director general of Unicef.