Immunogenicity of a Japanese encephalitis chimeric virus vaccine as a booster dose after primary vaccination with SA14-14-2 vaccine in Thai children.

BACKGROUND:Japanese Encephalitis chimeric virus vaccine (JE-CV) and SA14-14-2 vaccine are live-attenuated JE vaccines produced from the same virus strain. Data on interchangeability is limited. OBJECTIVES:To evaluate the immunogenicity and safety of JE-CV booster after primary vaccination with SA14-14-2 vaccine. METHODS:This study was an open-label clinical trial in Thai children who had received a primary SA14-14-2 vaccination at 12-24monthsbefore enrollment (ClinicalTrials.gov NCT02602652). JE-CV was administered. A 50% plaque reduction neutralization test (PRNT50) against three virus strains; JE-CV, SA-14-14-2andwild-type JE virus was measured before and 28-days post vaccination. The laboratory was performed at PRNT50 titers ⩾10 (1/dil) were considered seroprotective against JE. Geometric mean titer (GMT) of PRNT50 was calculated. Adverse events were observed for 28days. RESULTS:From March 2014 to June 2015, 50 children (64% male) were enrolled. Mean age and duration after primary vaccination was 26.9 (SD 4.6) and 12.8 (SD 2.7) months, respectively. The proportion of participants who had PRNT50pre and post-booster vaccination were 92% and 96% against JE-CV virus, 56% and 98% against SA-14-14-2 strain and 70% and 98% against wild-type JE virus, respectively. Solicited injection site reactions including erythema, pain and swelling occurred in 18%, 10% and 4% of subjects, respectively. Four children (8%) had fever (⩾37.7Celsius). Eight children (16%) had adverse events, which were not related to the vaccine. CONCLUSIONS:AJE-CV booster dose is highly immunogenic and safe among children who previously received SA14-14-2 vaccine.