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 12–24 months before enrollment (ClinicalTrials.gov NCT02602652). JE-CV was administered. A 50% plaque reduction neutralization test (PRNT 50 ) against three virus strains; JE-CV, SA-14-14-2 and wild-type JE virus was measured before and 28-days post vaccination. The laboratory was performed at PRNT 50 titers ⩾10 (1/dil) were considered seroprotective against JE. Geometric mean titer (GMT) of PRNT 50 was calculated. Adverse events were observed for 28 days. 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 PRNT 50 pre 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 (⩾37.7 Celsius). 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. [ABSTRACT FROM AUTHOR]