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

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.