Current Japanese encephalitis vaccines are derived from strains of genotype III, yet
heterologous genotypes are emerging in endemic areas. Inactivated vaccines given to
European travelers were found to elicit protective levels of neutralizing antibodies
against heterologous strains of genotypes I–IV.
Background: The role of children in SARS-CoV-2 transmission is unclear. We investigated two COVID-19 school exposure incidents in the Helsinki area.
Methods: We conducted two retrospective cohort studies after schools exposures, with a household transmission extension. We defined a case as an exposed person with either a positive RT-PCR, or positive microneutralisation testing (MNT) as confirmation of SARS-CoV-2 nucleoprotein IgG antibodies detection via fluorescent microsphere immunoassay (FMIA). We recruited close school contacts and families of school cases, calculated attack rates (AR) on school level and families, and identified transmission chains.
Findings: In incident A, the index was a pupil. Participation rate was 74% (89/121), and no cases were identified. In incident B, the index was a member of school personnel. Participation rate was 81% (51/63). AR was 16% (8/51): 6 pupils and 1 member of school personnel were MNT and FMIA positive; 1 pupil had a positive RT-PCR, but negative serology samples. We visited all school cases' families (n=8). The AR among close household contacts was 42% (9/20 in 3/8 families) but other plausible sources were always reported. At three months post-exposure, 6/8 school cases were re-sampled and still MNT positive.
Interpretation: When the index was a child, no school transmission was identified, while the occurrence of an adult case led to a 16% AR. Further cases were evidenced in 3 families, but other transmission chains were plausible. It is likely that transmission from children to adults is limited.
Funding: The Finnish Institute for Health and Welfare funded this study.
The new Japanese encephalitis vaccine (JE-VC, Ixiaro) has replaced mouse brain–derived vaccines (JE-MB) associated with serious safety concerns. A single dose of JE-VC effectively boosted immunity in JE-MB–primed travelers. Current recommendations for booster vaccination should be reevaluated.
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