Neutralizing antibody response to Japanese encephalitis inactivated mouse brain vaccine among laboratory personnel.

Among vaccinees given two doses of JE Nakayama strain liquid vaccine, 41.8% had significant neutralizing (N) antibody response to the P20778 strain and 48.6% to the Japanese Nakayama strain. Among vaccinees who received three doses of the freeze-dried vaccine, the proportion of positive reactors was 53.8% when the sera were tested with the P20778 strain and 47.4% with the Nakayama strain. A fairly large proportion of those vaccinees who had responded positively to the latter vaccine were found to have lost detectable N antibodies to the P20778 strain and a smaller proportion to the Nakayama strain 13 to 17 months after the third dose of vaccine. Following the administration of a booster dose of the vaccine after this time interval, 65.2% and 56.5% of vaccinees responded positively to the P20778 strain and the Nakayama strain, respectively. The differences between the proportion of positive reactors to the two strains were not significant either for the liquid vaccine or the freeze-dried vaccine. An important finding was the priming effect of infection with West Nile (WN) virus before vaccination. Those vaccinees who had N antibody to WN virus before vaccination had a significantly higher N antibody response to the P20778 strain of JE virus than those who had no detectable antibody to WN virus. These findings indicate that the JE Nakayama strain vaccine would be efficacious in India, particularly in view of the widespread prevalence of WN virus infection.

Serological response to Japanese encephalitis vaccine in a group of school children in South Arcot district of Tamil Nadu.

A trial with Biken Japanese encephalitis (JE) vaccine made in Japan was carried out in South Arcot district of Tamil Nadu state, India. A total of 113 school children were included in the trial. The efficacy (as determined by serological response) and safety of the vaccine were evaluated. Side effects, though minor, were noted in 54.9 per cent of the children after each dose. The serum antibody titres were determined by mouse neutralization test, plaque reduction neutralization test and haemagglutination inhibition test. An antibody response to two-dose primary vaccination schedule was observed in 72.7 per cent, whereas 87.8 per cent of the vaccines responded positively after the booster dose administered one year after. Only about 20 per cent of the children had persisting antibodies one year after the primary vaccination. The results indicated a probable need of the third dose in the primary vaccination schedule.