Orthopoxvirus Seroprevalence and Infection Susceptibility in France, Bolivia, Laos, and Mali

Abstract

To determine a demographic overview of orthopoxvirus seroprevalence, we tested blood samples collected during 2003-2019 from France (n = 4,876), Bolivia (n = 601), Laos (n = 657), and Mali (n = 255) for neutralizing antibodies against vaccinia virus. In addition, we tested 4,448 of the 4,876 samples from France for neutralizing antibodies against cowpox virus. We confirmed extensive cross-immunity between the 2 viruses. Seroprevalence of antibodies was <1% in Bolivia, <5% in Laos, and 17.25% in Mali. In France, we found low prevalence of neutralizing antibodies in persons who were unvaccinated and vaccinated for smallpox, suggesting immunosenescence occurred in vaccinated persons, and smallpox vaccination compliance declined before the end of compulsory vaccination. Our results suggest that populations in Europe, Africa, Asia, and South America are susceptible to orthopoxvirus infections, which might have precipitated the emergence of orthopoxvirus infections such as the 2022 spread of monkeypox in Europe.

Keywords: Bolivia; France; Laos; Mali; Orthopoxvirus; cowpox virus; monkeypox virus; seroprevalence; sexually transmitted infections; vaccinia virus; viruses; zoonoses.

Figure

Antibody titers and percentage of population positive for antibodies against orthopoxviruses in France in study of seroprevalence and infection susceptibility in France, Bolivia, Laos, and Mali. Serum samples from 4,448 persons were tested for antibodies against both vaccinia and cowpox virus and an orthopoxvirus neutralization titer (ONT) was determined. A, B) Overall comparison of ONT geometric mean ±SD (A) and percentage of positive participants (ONT>20) (B) according to decade of birth (p values are described in Appendix Table 1). C, D) Comparisons of ONT geometric mean ±SD (C) and percentage of positive persons (ONT>20) (D) between male and female participants according to decade of birth. E, F) Comparisons of ONT geometric mean ±SD (E) and percentage of positive persons (ONT>20) (F) for populations in 4 different regions of France according to their decade of birth (p values are described in Appendix Table 2). Mann-Whitney tests were used to determine geometric means ±SD; Fisher exact tests were used to compare percentage of positive persons. A p value <0.05 was considered significant.