The efficacy of mouse-brain inactivated Nakayama strain Japanese encephalitis vaccine--results from 30 years experience in Taiwan.

An intensive mandatory vaccination program has been underway, combating Japanese encephalitis (JE) since 1968 in Taiwan. Long-term collection of immunization records has been developed from 1967 to 2000 in this study to retrospectively assess the efficacy of the mouse-brain inactivated Nakayama JE vaccine. The vaccine efficacy (VE) of completing at least two doses of the JE vaccine was 96.98%. Among 1 to 14-year-old children, the efficacy of completing 1, 2, and 3 doses of immunization was 85.59%, 91.07% and 98.51%, respectively. Furthermore, the long-term efficacy for a single dose vaccinated at least 25 years was 86.79%, and for 2 and 3 doses it was 88.10% and 95.54%, respectively. In contrast to previous studies that recommended at least two doses of JE vaccination to acquire necessary protection, the empirical results in this study indicated that even immunization with one single dose provides sufficient protection to the population. However, a single dose of JE vaccine might still be beneficial for some JE epidemic or endemic developing countries with limited resources for infectious disease control.