Serological Response of Japanese Children and Old People to Japanese B Encephalitis Mouse Brain Vaccine

Abstract

Summary

Japanese children, 3 to 5 years old, and people, over 60 years of age, living in the endemic region of Okayama, Japan, were given commercial Japanese B encephalitis mouse brain vaccine—2 doses of 1 cc each, 6 days apart, and a 3rd dose of 1 cc one month after the first dose in advance of the season when outbreaks of the disease may be expected. None of the children had antibodies before vaccination, and of the 10, who were inoculated with a vaccine having a 50% immunogenic dose (ID₃₀) of 0.013 cc by mouse assay, all had neutralizing antibodies 10 days after the 3rd dose, while only 1 of the 10, who received a vaccine with an ID₅₀ of 0.077 cc, developed a significant neutralization index. However, in a group of 7 old people, without antibodies before inoculation, who received the same dosage of the better vaccine (ID₃₀ of 0.013 cc) none developed neutralizing or complement-fixing antibodies. Complement-fixing antibodies for the mouse brain component appeared as well as for the Japanese B virus contained in the vaccine, but in 5 of the 10 children, inoculated with the better vaccine, the titers were significantly higher with the Japanese B antigen. Complement-fixing antibodies, specific for the Japanese B virus, appeared rapidly in all of the 10 old people who had neutralizing antibodies (evidence of previous inapparent infection) prior to inoculation, but in none of the 9 old people who were without such antibodies.