INTERVIEW. Risk of Mpox epidemic in France: “The Clade 1b strain seems to be more contagious than the previous ones”

A first case of the new Mpox variant (also called monkeypox) was identified in France on Monday January 6. The health authorities want to be reassuring about the risk of infection for the general population but point out preventive measures for target audiences. Explanations with Étienne Decroly, virologist and research director at the CNRS.

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Should we fear an Mpox epidemic in France?

The circulation of the virus is closely monitored by health authorities, who have put in place relatively important public health tools that make it possible to control infection, in particular by effectively isolating patients to limit the spread. However, with the appearance in the territory of the Clade 1b strain, which seems to be more contagious than the previous ones, it may be necessary to strengthen public health recommendations. Particularly regarding the vaccination of populations at risk.

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Exactly, how is the Mpox clade 1b virus transmitted?

Transmission of Mpox via the clade 1b variant can occur by direct contact with bodily fluids during sexual intercourse, but also with skin lesions (wounds, scabs) of an infected person.

However, if in Africa the epidemic is relatively significant, the spread of the virus in Europe is limited to date: a few cases have been recorded in Sweden, Germany, the United Kingdom and Belgium in 2024. In France, 215 cases infections were recorded last year (all linked to another variant, called clade 2, Editor's note), to which is now added the person contaminated by clade 1b in recent days.

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With this strain, are the symptoms different?

No, the symptoms have not changed and begin with fever and muscle pain. Two weeks after exposure to the virus, skin lesions appear on the skin and can spread. They are symptomatic of the disease and can easily be identified by a doctor or dermatologist. Typically, the infection resolves spontaneously in about two weeks. But of course it happens that the patient develops more serious forms of the disease, such as superinfections.

Which populations are most at risk?

Those most at risk are mainly men who have sex with men and people with multiple sexual partners. Populations under 55 who have not completed their vaccination schedule are also more exposed. I say this because older people were normally vaccinated against smallpox when they were younger. They therefore have residual acquired immunity against this virus.

How to limit the spread of the Mpox virus?

Health authorities recommend that people at high risk of exposure to the virus, that is, those who have had close contact with an infected person or who may have multiple sexual partners, get preventive vaccinations.

This recommendation also applies to immunocompromised people. Vaccination is free and offers effective coverage (85% effectiveness according to data from the Vaccination info service site). Of all the cases of infection recorded in France last year, we know that at least 107 people were not immune to the virus.