Duration of Neutralizing Antibody Titer after Japanese Encephalitis Vaccination

In paired serum samples collected from 17 children, we measured neutralizing antibody (NTAb) titers after the second series of routine Japanese encephalitis (JE) vaccination in Japan to estimate the duration of NTAb titer when children did not receive the third series of routine vaccination by applying a random coefficient model. We also measured NTAb titers in adult serum samples to confirm the duration of NTAb titer estimated in the analysis of pediatric serum samples. In the absence of the third series of routine vaccination, 18% (3/17), 47% (8/17), 82% (14/17) and 100% (17/17) of children were estimated to become NTAb negative at 5, 10, 15, and 20 years after the second series of routine vaccination, respectively. Of 38 adults, 39.5% (15/38) became NTAb negative; the percentage was somewhat lower than that of antibody-negative children. The results suggested that JE vaccination schedule should be reevaluated in the future.