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

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Abstract
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[long dash]2 doses of 1 ml. each, 6 days apart, and a 3d dose of 1 ml. one month after the 1st 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 (ID50) of 0.013 ml. by mouse assay, all had neutralizing antibodies 10 days after the 3d dose, while only 1 of the 10, who received a vaccine with an ID60 of 0.077 ml., 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 (ID50 of 0.013 ml.), 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.