Susceptibility to monkeypox virus infection: seroprevalence of orthopoxvirus in 4 population samples; France, Bolivia, Laos and Mali.

Europe is experiencing an epidemic of monkeypox virus against a background of limited knowledge of population immunity to orthopoxviruses. We tested antibodies neutralizing vaccinia virus in blood samples from Bolivia (n=601), Laos (n=657), Mali (n=255) and France (n=4876). We also tested neutralization of cowpox virus in 4448 French samples, which confirmed extensive cross-immunity between both viruses. Using a cut-off titer of 20, seroprevalence is <1% in Bolivia, <5% in Laos (mainly related to vaccination in the elderly), 17.25% in Mali (related to both smallpox vaccination and the likely natural circulation of orthopoxviruses). In France, neutralizing antibodies are found (but at low prevalence) in age groups supposed to be vaccinated, suggesting both decrease in antibody titer in vaccinated individuals and decline in smallpox vaccine compliance before the end of compulsory vaccination. We conclude that the populations tested in Europe, Africa, Asia and South-America are massively susceptible to orthopoxvirus (e.g. monkeypox) infections. Article summary lineSeroprevalence of orthopoxvirus tested on 4 continents is very low, even for people born before the eradication of smallpox, making populations vulnerable to the emergence of zoonotic orthopoxviruses such as monkeypox virus.