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

Abstract

Summary

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 cc each 4 to 5 days apart and the 3rd dose of 1 cc one month after the first dose. The vaccine used for the first dose had a 50% im-munogenic dose (ID₅₀) of 0.028 cc by mouse assay, which is considerably less than the minimal required potency of 0.01 cc, and the lot used for the other 2 doses just fulfilled the minimal requirements with an ID₅₀ of 0.0094 cc. The results in 20 Americans, aged 19 to 35, who were stationed in Tokyo and were without antibody or previous history of having received¹ this vaccine, were as follows:

(a) 15% had neutralizing antibodies 10 days after the 2nd dose, and 45% 10 days after the 3rd dose.

(b) Only 2 men (10%) developed specific complement-fixing antibodies for the Japanese B virus, which appeared after the 2nd 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 2nd dose and in 45% after the 3rd dose of vaccine.

The antibody response in this group of Americans in Japan, vaccinated by the triple-dose method with commercial preparations, which either just fulfilled or were below the ID₅₀ of 0.01 cc which is the minimal requirement of potency, was about the same after the 3rd dose as that previously obtained after the 2nd dose in a group of 25 Americans, of similar age in the U.S.A., who received 2 doses of 2 cc each, 3 days apart, of a freshly prepared vaccine with an ID₅₀ of 0.0055 cc.