Measles elimination and immunisation: national surveillance trends in Japan, 2008-2015.

Measles elimination relies on vaccination programmes. In Japan, a major outbreak started in 2007. In response, 5-year two-dose catch-up vaccination programme was initiated in April 2008 for children 13-16-years-old. In this study, we analysed the epidemic curves, incidence rates for each age group, virus genotype, vaccination coverage and ratio of measles gelatin particle agglutination (PA) antibody using surveillance data for 2008-2015. Monthly case counts markedly decreased as vaccination coverage increased. D5, which is the endemic virus type, disappeared after 2011, with the following epidemic caused by imported viruses. Most cases were confirmed to have a no-dose or single-dose vaccination status. Although the incidence rate among all age groups ⩾5-years-old decreased during the study period, for children <5-years-old, the incidence rate remained relatively high and increased in 2014. The ratio of PA antibody (⩾1:128 titres) increased for the majority of age groups, but with a decrease for specific age groups: the 0-5 months and the 2-4, 14, 19 and most of the 26-55- and the 60-year-old groups (-1 to -9%). This seems to be the result of higher vaccination coverage, which would result in decreasing natural immunity booster along with decreasing passive immunity in infants whose mothers did not have the natural immunity booster. The 20-29- and 30-39-year-old age groups had higher number of cases, suggesting that vaccination within these age groups might be important for eliminating imported viruses.