ABSTRACT
The immune status of 40 volunteers who received the full course of Japanese encephalitis (JE) vaccine a year earlier and 15 individuals who had received only a booster dose at the same time, was studied by estimating the level of persistence of protective antibody in the sera. All the sera showed persistence of 100 per cent seroconversion rate. Individuals who had the full course of vaccination still had high levels of antibody (mean 2.8 Iog10); however there was a fall of 0.8 Iog10 from the post-booster level. Volunteers who had received only a booster dose, also showed persistence of high level of protective antibody (mean 2.4 Iog10), a drop of 0.9 Iog10 from the post-booster level. Neutralizing (N) antibody estimated using Dibrugarh (7812474) strain of JE virus also demonstrated persistence of high level of protective antibody against this virus (mean 2.4 Iog10). Persistence of high level of protective antibody against homologus and heterologus (Dibrugarh) virus strains and absence of vaccine related side-effects even one year after administration of JE vaccine produced in India, demonstrates the immunizing potency and safety of this new vaccine.