A multi-prefecture rubella outbreak associated with technical intern training for foreign workers in Japan, 2016: Implications for sustaining rubella elimination verified in 2025.

Abstract

Rubella elimination in Japan was verified in September 2025; however, importation and immunity gaps can still precipitate outbreaks. We investigated a multi-prefecture rubella outbreak in 2016 linked to an introductory training course for foreign workers. After a rubella case was reported in Saitama Prefecture on June 6, 2016, we investigated the training facility and conducted active nationwide surveillance. We collected roster and dispatch information, monitored cases reported to the National Epidemiological Surveillance of Infectious Diseases, and interviewed trainees, host-company staff. Ninety-two trainees were dispatched to 41 companies in 23 prefectures. Thirteen rubella cases were identified. Ten patients were Vietnamese trainees, nine were likely infected during group training, and one was suspected to have imported rubella from Vietnam. Three individuals were likely infected at host companies, including two Japanese supervisors. No patient had documented records of a rubella-containing vaccine. Viruses from three cases belonged to genotype 2B. A single importation into a congregate training setting can rapidly create multi-prefecture exposure. Vaccination and/or verification of immune status among incoming trainees and susceptible host-company workers is essential to prevent similar events and sustain rubella elimination in Japan.