Neutralizing and Complement-Fixing Antibodies for Japanese B Encephalitis Virus in Vaccinated U. S. Personnel in Japan

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Abstract
Commercial Japanese B encephalitis mouse brain vaccine was administered to the occupation forces in Japan in 1946 by the triple-dose method, and the antibody response was studied in a group of men who received the first 2 doses of 1 ml. each, 4-5 days apart and the 3d dose of 1 ml. one month after the 1st dose. The vaccine used for the 1st dose had a 50% immunogenic dose (ID50) of 0.028 ml. by mouse assay, which is considerably less than the minimal required potency of 0.01 ml. and the lot used for the other 2 doses just fulfilled the minimal requirements with an IDso of 0.0094 ml. The results in 20 Americans, aged 19 to 35, who were stationed in Tokyo and were without antibody or previous history of having received this vaccine, were as follows: (a) 15% had neutralizing antibodies 10 days after the 2d dose, and 45% 10 days after the 3d dose. (b) Only 2 men (10%) developed specific complement-fixing antibodies for the Japanese B virus, which appeared after the 2d dose of vaccine, (c) Complement-fixing antibodies for the mouse brain component of the vaccine appeared in original serum dilutions of 1:2 to 1:4 in 35% after the 2d dose and in 45% after the 3d dose of vaccine. The antibody response in this group of Americans in Japan, vaccinated by the triple-dose method with commercial prepns., which either just fulfilled or were below the ID60 of 0.01 ml. which is the minimal requirement of potency, was about the same after the 3d dose as that previously obtained after the 2d dose in a group of 25 Americans, of similar age in the U.S.A., who received 2 doses of 2 ml. each, 3 days apart, of a freshly prepd. vaccine with an ID50 of 0.0055 ml.