Abstract
A number of junior high school students living in northern Hokkaido, where Japanese encephalitis (JE) is not prevalent, were inoculated with inactivated JE virus vaccines different in potency and antigenicity to study the production of antibody by the vaccination per se.
Following results were obtained;
1) The three lots of mouse brain Nakayama vaccines differed greatly in their antibody-producing capacities.
The capacity was the highest in the Lot 3 vaccine, the next highest was the Lot 2, and the lowest was Lot 1.
2) The antibody-producing capacity of the two JaGAr type vaccines, the mouse brain JaGAr and the tissue cultured Mukai, was remarkably lower than that of any lot of the three Nakayama vaccines. However, considerable antibody increase was achieved even by the JaGAr type vaccines, when the vaccines were inoculated twice with different intervals of time.
3) The booster effect on antibody response of the mouse brain Nakayama vaccine inoculated one year after the first vaccination was striking.
The antibody thus produced was maintained as high as 1:40 to 1:2560 even after one year of the booster vaccination.
4) The presence in serum of minimal amount of neutralizing antibody produced by initial vaccination stimulated greatly antibody production following subsequent vaccination. This emphasizes that the efficacy of JE vaccine for man should be investigated for those persons living in the area free of the virus.
5) Inoculation of the Nakayama vaccine produced antibody to heterologous JaGAr strain as well as to homologous Nakayama strain.
The heterologous antibody thus produced was one nineth to one-sixteenth in the titer of homologous antibody. This implies that the Nakayama antibody of 1:160 or higher in titer may be necessary to prevent infection with JaGAr type virus.
6) The neutralizing antibody obtained by the vaccination increased proportionally with the rise in hemagglutination-inhibition (HI) antibody, but the former antibody below 1:80 in titer could not be detected by the HI test.
