Most French infants lack antibodies to EV-A71, a virus tied to severe childhood disease

Two enteroviruses that can cause serious illness in young children circulate very differently through France's paediatric population, a Eurosurveillance study published this week reports — and for one of them, the youngest and most vulnerable infants are largely unprotected [s1]. Enterovirus A71 (EV-A71) and enterovirus D68 (EV-D68) are both linked to severe clinical conditions, especially in infants and young children, but until now population susceptibility to either virus in France was unknown [s1].

To close that gap, researchers tested neutralising antibodies — the kind that block infection — in 501 serum samples collected between 2023 and 2025 from people under 18 across metropolitan France [s1]. The samples were drawn using a stratified approach by sex, age and region, and tested against an EV-A71 sub-genogroup C1 strain and an EV-D68 subclade B3 strain, both isolated in 2016 [s1]. Testing for neutralising antibodies — rather than simpler assays that detect any prior exposure — is a deliberately conservative choice, because it measures the antibodies thought to actually block infection and so comes closest to gauging real protection [s1].

A wide gap between the two viruses

The overall picture split sharply by virus. For EV-A71, the estimated seroprevalence was 43.7% (95% confidence interval 39.3–48.2) — meaning well under half of children and adolescents carried protective antibodies [s1]. For EV-D68, it reached 96.0% (95% CI 93.9–97.5), near-universal immunity across the paediatric population [s1]. Neither virus showed a meaningful difference by sex [s1].

The contrast matters most at the youngest ages. EV-A71 seropositivity varied significantly by age group (p = 0.002) and by area of residence (p < 0.001), the kind of patchy, uneven immunity that leaves pockets of susceptible children [s1]. The starkest figure concerns the very youngest: 23 of 25 children under one year of age lacked protective EV-A71 antibodies [s1]. EV-D68 immunity, by contrast, was high and even across all paediatric age groups, with no comparable geographic variation [s1]. The divergence likely reflects how and when each virus circulates: near-universal, early exposure to EV-D68 leaves almost every child immune, whereas more uneven EV-A71 transmission leaves protection patchy and concentrated in older children who have had time to encounter it [s1].

Antibody strength followed its own age gradient. Neutralising antibody titres differed significantly by age for both viruses — EV-A71 (p = 0.004) and EV-D68 (p < 0.001) — with the highest titres for EV-A71 among one- to under-two-year-olds, and for EV-D68 among those under one year [s1].

Why susceptibility in the under-ones is the headline

EV-A71 is best known as a cause of hand, foot and mouth disease, but it is the virus's rarer complications that make its epidemiology worth tracking: it can cause neurological disease, including brainstem encephalitis, and the most serious outcomes fall disproportionately on infants and toddlers. A population in which most newborns and infants have no neutralising antibodies is, in the authors' framing, a population at potential risk of severe disease should transmission intensify [s1].

EV-D68 presents the opposite situation. The study found a high level of immunity against it across every paediatric age group [s1]. That near-universal exposure is itself a reminder of how widely the virus has circulated — EV-D68 has been associated with severe respiratory illness and, in rare cases, acute flaccid myelitis, a polio-like paralysis — but the serology suggests that by adolescence, and indeed well before it, most French children have already encountered it.

The authors are measured about what a seroprevalence snapshot can and cannot establish. It describes the immune landscape — who is susceptible and who is not — rather than predicting an outbreak [s1]. The strains used for testing were isolated in 2016, and antibody levels measured in a laboratory are a proxy for, not a guarantee of, real-world protection. What the study does deliver is a baseline: a first estimate of how exposed France's children are to two viruses that had, until now, no population immunity data at all, and a clear signal that for EV-A71 the gap sits precisely where the disease is most dangerous — in the first year of life [s1]. That is the kind of groundwork that lets surveillance systems, and any future vaccine strategy, know which children to watch and where [s1].

This article is informational and is not medical advice.