Neutralizing Antibody Persistence in Pediatric Travelers from Non-JE-endemic Countries Following Vaccination with IXIARO® Japanese Encephalitis Vaccine: An Uncontrolled, Open-label Phase 3 Follow-up Study

Background: In an initial study among children from non-Japanese encephalitis (JE)-endemic countries, seroprotection rates remained high 6 months after completion of the primary series with IXIARO®.

Methods: In this open-label follow-up study, a subset of 23 children who received a 2-dose primary series of IXIARO® in the parent study, were evaluated for safety and neutralizing antibody persistence for 36 months.

Results: Seroprotection rates (SPRs) remained high but declined from 100% one month after primary immunization to 91.3% at month 7 and 89.5% at month 36. Geometric mean titers (GMTs) declined considerably from 384.1 by day 56-60.8 at month 36. No long-term safety concerns were identified.

Conclusions: The substantial decline in GMT observed in this study, together with previously published data on children vaccinated with IXIARO® support the recommendation for a booster dose in children who remain at risk of JE from 1 year after the primary series of IXIARO®, consistent with the recommendation for adults.

Clinical Trial Registry Number: NCT01246479.