Seroprevalence of EV-A71 and EV-D68 antibodies in the paediatric and adolescent population, France, 2023 to 2025

BACKGROUNDEnteroviruses (EV)-A71 and EV-D68 are potentially associated with severe clinical conditions, especially in infants and young children. Population susceptibility to these viruses is unknown in France.AIMWe sought to estimate seroprevalence of EV-A71 and EV-D68 neutralising antibodies (nAbs) among children and adolescents living in France.METHODSA stratified sampling approach based on sex, age and geographical area of residence was applied to obtain sera for routine diagnostic from ˂ 18-year-olds in metropolitan France. A total of 501 serum samples collected between 2023 and 2025 from 0-17-year-olds were included in the investigation. Neutralising activity was tested against EV-A71 sub-genogroup C1 and EV-D68 subclade B3 strains isolated in 2016, allowing to determine seropositivity and nAb titre. Data were analysed overall, by sex, age group and geographical area.RESULTSFor EV-A71, the overall estimated seroprevalence was 43.7% (95% CI: 39.3-48.2) while for EV-D68 this reached 96.0% (95% CI: 93.9-97.5). No differences according to sex were observed. Unlike EV-D68, EV-A71 seropositivity rate varied significantly by age group (p = 0.002) and area of residence (p < 0.001). Notably, 23 of 25 children aged ˂ 1 year lacked EV-A71 protective antibodies. Concerning nAb titres, significant differences occurred across age groups both for EV-A71 (p = 0.004) and EV-D68 (p < 0.001). The nAb titres appeared as highest in 1 to under-2-year-olds for EV-A71 and 0 to under-1-year-olds for EV-D68.CONCLUSIONThis seroprevalence study in France reveals a high proportion of newborns and infants susceptible to EV-A71 at potential risk of severe disease, contrasting with the high level of immunity against EV-D68 across all paediatric age groups.