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This study evaluated the effect of a booster vaccination of a new, live attenuated, Japanese encephalitis chimeric vaccine (JE-CV). Previously this vaccine has been used as a booster 12 months after priming with an inactivated vaccine and at >24 months after priming with the same JE-CV. This study evaluates the immunogenicity and safety of the JE-CV given at 12–24 months after JE-CV priming.Phase III, open-label study in the Republic of Korea in which 119 children previously vaccinated with JE-CV at 12–24 months of age received a JE-CV booster at 12–24 months after primary vaccination. JE neutralizing antibody titers were measured using >50% plaque reduction neutralization test prebooster and 1 month postbooster vaccination. Seroprotection (SP) was defined as ≥10 (1/dil). Safety was assessed for 28 days postvaccination by parental reports. Serious adverse events were monitored for 6 months postvaccination.Antibody persistence was high prebooster (SP rate 93.5%). There was a strong anamnestic response postbooster vaccination, with an SP rate of 100% and a >50-fold increase in geometric mean titer from the prebooster level. Both antibody persistence and the booster response were independent of whether the booster was given at 12–17 or 18–24 months. The safety profile was good and comparable with the primary vaccination; there were no vaccine-related serious adverse events and no deaths.This study confirms the suitability of a JE-CV booster vaccination at 12–24 months after a primary dose of the same vaccine given at 12–24 months of age in children in the Republic of Korea.