Effect of current Japanese encephalitis vaccine on different strains of Japanese encephalitis virus.

Inactivated Japanese encephalitis (JE) vaccine was given to healthy children and their neutralizing antibody titres against nine JE virus strains were measured. After two shots of the vaccine in the first year, most of the children showed seroconversion, but their neutralizing antibody titres were not high, and one year after vaccination their titres had decreased to low levels. However, a booster dose of vaccine in the second year had a marked effect on the antibody response. The neutralizing antibodies induced by the vaccine reacted to almost the same extent with nine different JE virus strains, though significantly higher titres against the Nakayama strain, the vaccine strain, were observed after vaccination in the second year.