Neutralization antibody responses induced by Japanese encephalitis virus vaccine.

Single doses of Japanese encephalitis (JE) vaccine of the Nakayama strain were given to members of the staffs of a hospital and 99 paired-sera were obtained. Neutralization antibody titers of the sera were determined against the Nakayama strain and E-50 strain, isolated from wild Culex tritaeniorhynchus using clone C6/36 of Singh's Aedes albopictus mosquito cell culture. Post-vaccination sera showed a significant neutralizing antibody response against both the Nakayama and E-50 strain. The geometrical mean neutralization titers of post-vaccination sera against the Nakayama and E-50 strains were in the same order, although the geometrical mean neutralization titer against the Nakayama strain was the higher in pre-vaccination sera. The antibody responses against the Nakayama strain and E-50 strain were somewhat different in detail: 7 individuals with a pre-vaccination neutralization titers of less than 10 showed antibody responses to the Nakayama strain, whereas 3 individuals of the same group did not show any detectable response to the E-50 strain.