Evidence of the Partial Effects of Inactivated Japanese Encephalitis Vaccination: Analysis of Previous Outbreaks in Japan From 1953 to 1960

Purpose To evaluate the partial effects of vaccination against equine Japanese encephalitis (JE) and characterize other prognostic factors based on previous outbreak records in Japan from 1953 to 1960. Methods Individual case records, which included demographic information, vaccination history, and clinical information (dates of onset, recovery and death, and symptoms), were investigated. The relations between two outcomes, JE death and symptomatic period, and other variables were examined. Results Of a total reported 803 cases during the observation period, 453 (56.5%) were diagnosed with either serological, histopathological, or epizootiological methods. Vaccination (adjusted odds ratio = 0.77, 95% confidence interval: 0.61, 0.97) and an older age (adjusted odds ratio = 0.83, 95% confidence interval: 0.71, 0.96) significantly reduced the risk of JE death. The symptomatic period was also significantly shortened with vaccination (p < 0.001). Conclusions The risk of JE death was lowered and the symptomatic period of survivors shortened with inactivated JE vaccination. These findings demonstrate the partial effects of vaccination in reducing the burden of this disease.