Retention of neutralizing antibodies to Japanese encephalitis vaccine in age groups above fifteen years in Korea

BACKGROUND: The incidence of Japanese encephalitis (JE) has markedly decreased after the national immunization program in Korea, but still reported intermittently in adults. Prospective studies are required to determine whether JE virus (JEV)-neutralizing antibody (NAb) levels decline with age after the final JE vaccination. In this study, we evaluated the titers of NAbs against JEV in Korean adolescents and adults. METHODS: Specimens were collected from normal, healthy individuals aged 1 to >70 years (a total of 1,605 cases) from five regional hospitals in Korea. Neutralizing antibody (NAb) titers were determined using a pseudotyped JEV NAb assay. RESULTS: The JEV NAb-positive population was >95% in the 15-29 year age group, 89.42% in the 30-44 year age group, 75.24% in the 55-59 years age group, and 59.77% in the ≥70 year age group. NAb titers from the 20 to 70 year age groups showed a progressive decrease in proportion to age (P < 0.0001). CONCLUSIONS: The retention of NAbs after the final JE vaccination in childhood is a key indicator of the vaccination program and will have a significant impact on future JE prevention strategies.