Detection of Measles Virus Genotypes B3, D4, D5, D8, and H1 in the Surveillance System in Hokkaido, Japan, 2006-2015, the Last Decade toward the Elimination.

Measles is an acute and highly contagious disease caused by measles virus (MeV). The government of Japan, following the last epidemic in 2007 and 2008, which was caused by genotype D5 strains, introduced a catch-up-vaccination program for teenagers during Japan fiscal years 2008-2012 and a mandatory case-based reporting system for the nationwide elimination. Furthermore, laboratory confirmation of measles cases by genotyping of isolates has been performed to clarify the source of infection and support the interruption of measles cases. Owing to these preventive measures, the number of measles cases has been steadily decreasing after the last epidemic. In March 2015, Japan was internationally verified as having achieved measles elimination by the World Health Organization Regional Office for the Western Pacific. The continuous elimination of measles and high levels of vaccination coverage for MeV have been maintained nationally. However, imported or import-associated cases of measles have sporadically occurred during this time. After the last nationwide epidemic, 17 imported or import-associated measles cases (MeV strains identified as genotypes H1, D4, D8, and B3) were reported in Hokkaido, the northern islands of Japan. In this study, we present the occurrence of measles and surveillance activities in Hokkaido during 2006-2015.