Immunisation against Japanese encephalitis in Nepal: experience of 1152 subjects.

During the summer of 1983, 1152 subjects were immunized against Japanese Encephalitis at BMH Dharan. This was the first use of the BIKEN killed lyophilised vaccine in the British Army. Three doses of 1 ml (0.5 ml for children under 3 years) given 10 days apart produced a protective neutralizing antibody response (titre more than 1:10) in almost 90% of subjects. Two doses of vaccine however seemed inadequate in that less than 40% of subjects seroconverted. Side-effects were minimal and trivial. Studies of neutralizing antibodies before vaccination showed up to 30% of Nepalese subjects tested were already immune due to previous inapparent infection while all but one of the British Nationals were fully susceptible.