Exposure to H1 genotype measles virus at an international airport in Japan on 31 July 2016 results in a measles outbreak

In March 2015, the Measles Regional Verification Commission for the World Health Organization Western Pacific Region verified that Japan had achieved measles elimination (1) based on the verification criteria. (2) Only 35 confirmed measles cases were reported in 2015, and for 2016, measles activity was low until July (n = 16, as of 3 August). However, the number of reported measles cases surged in the middle of August 2016. Several cases were considered sporadic cases without a known source of infection or imported cases because they initially seemed to be unrelated. However, through vigilant daily monitoring of national surveillance data by surveillance officers at the national level, including fellows of the Field Epidemiology Training Program at the National Institute of Infectious Diseases, and their close communication with local public health staff, five cases were found to have been present at a large international airport on the same day as a possible index case was found