A total of 368 blood specimens were resampled from a serum
collection containing 2914 blood
samples which were collected by a random sampling in Taiwan in 1991. The
plaque reduction
neutralization test was applied to evaluate the neutralizing ability to
two strains of Japanese
encephalitis viruses, i.e. Nakayama (the present vaccine strain) and JE5
(a Taiwan isolate). The
result revealed that antibodies against JE virus were present in each
stratified age group.
Antibody positive rates were both highest in the group older than 70
years although the lowest
rates were located in different groups. In addition, the result showed
that the immunogenicity
potency of the antibody induced by the vaccine strain did not have a
good coverage against
JE5. The rate of neutralizing antibodies above the level of protective
efficacy of the present
vaccine was limited as low as 37·93%. Efficacy of the vaccine
used at present was apparently
not efficient. Consideration of a more promising vaccine may be necessary.