It is a disease that seemed from another age in the West. On July 21, the United States reported its first case of poliomyelitis in almost ten years. The 20-year-old man affected resides in Rockland County, 30 miles from New York. He had gone to the hospital following a paralysis of the leg. Quickly diagnosed as being infected with poliovirus, the causative agent of the disease, he still suffers from partial paralysis. He was not vaccinated.
Rich countries had almost forgotten this highly contagious condition, caused by a virus that attacks the nervous system and can cause permanent motor disability. Its usual mode of transmission is the fecal-oral route, from contaminated water or food. Before the start of massive vaccination campaigns in the mid and late 1950s in the West, this disease sowed fear. Especially among parents of children under 5, the virus’s favorite targets. In France, between 1943 and 1988, polio caused 32,793 paralysis and killed 3,315 people.
Since 1988, the number of polio cases has plummeted by 99%. A spectacular drop, due to the deployment of the Global Polio Eradication Initiative, launched under the impetus of national governments, the World Health Organization, Rotary International, centers for control and prevention American Diseases and Unicef. She then received massive support from the Bill and Melinda Gates Foundation and Gavi, the Vaccine Alliance. Result: while in 1988, the number of cases was estimated at 350,000, with an endemic virus in more than 125 countries, only six cases of paralysis due to wild polioviruses were notified in 2021. Only two countries, the Afghanistan and Pakistan continue to experience polio outbreaks linked to the wild virus.
The young American, however, was not infected in one of these countries. His paralysis results from a disturbing fact, already observed elsewhere. The virus that struck him was derived from an oral vaccine used in many developing countries. A vaccine containing a poliovirus rendered harmless but still alive, which then mutated, because it multiplied in many unvaccinated people.
“A danger in New York”
The scenario is the following. A person receives one of these oral vaccines. She then excretes the poliovirus in her stool for several weeks. “If around her there are only people vaccinated orally, this virus will not find anyone to infect.says Maël Bessaud, poliovirus expert at the Pasteur Institute. But if she encounters many unvaccinated people, or if she goes to an area where only the inactivated vaccine is used, this virus may start circulating. » If it spreads for several months from one unvaccinated person to another, it can accumulate a lot of changes in its genome. It is then that it can become virulent again and cause paralysis.
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