Investigating the immunizing effect of the rubella epidemic in Japan, 2012-14.

ABSTRACT

OBJECTIVES: A rubella epidemic occurred in Japan from 2012-14, involving more than 15,000 cases. The present study aimed to estimate the immunizing effect of the epidemic, analyzing seroepidemiological data that were collected over time and age. METHODS: Annual nationwide cross-sectional surveys were conducted from July to September, collecting serum from at least 5,400 individuals. The proportions seropositive were estimated before (2012), during (2013) and after (2014) the epidemic. RESULTS: While the cases were mainly seen among men aged from 30-49 years, no significant increase was observed in the proportion seropositive in the corresponding age group. Even after the epidemic, age-standardized proportion seropositive of the total population remained 79.3% (95% confidence interval (CI) 75.2, 83.4) and that among males was as small as 76.7% (95% CI 73.8, 79.6). CONCLUSIONS: Susceptible pockets remain in Japan, exposing the country to risk of additional rubella epidemics.