Dubischar KL, et al. – Researchers sought to determine the immunogenicity of the inactivated Japanese encephalitis virus vaccine IXIARO in children from a Japanese encephalitis virus–endemic region. Findings demonstrated high immunogenicity of IXIARO at both doses tested in the pediatric population, leading to protective antibody titers at day 56 in >99% of subjects who received the age–appropriate dose.

Methods

• Age–stratified cohorts of children between 2 months and 17 years were provided 2 doses of Vero cell–derived inactivated Japanese encephalitis (JE) virus vaccine (IXIARO; Valneva Austria GmbH, Vienna, Austria) administered 28 days apart [<3 years, 0.25mL (half adult dose); ≥3years, 0.5mL (full adult dose)].
• For this study, immunogenicity endpoints were seroconversion rate, 4–fold increase in JE neutralizing antibody titer and geometric mean titer assessed 56 days and 7 months after the first vaccination in 496 subjects of the intent–to–treat population.
• Analysis of the immune response to JE virus at both time points was also performed in accordance to prevaccination JE virus and dengue virus serostatus.

Results

• At day 56, researchers observed seroconversion in ≥99.2% of subjects with age–appropriate dosing; there were reports of 4–fold increases in titer for 77.4%–100% in various age groups; geometric mean titers ranged from 176 to 687, with younger children having the strongest immune response.
• At month 7, 85.5%–100% subjects maintained seroconversion.
• Pre–existing JE virus immunity seemed having no impact on immune response at day 56; however, it resulted in a better persistence of protective antibody titers at month 7.