Although rubella is usually a mild, febrile illness, and up to 50% of rubella infections are asymptomatic, congenital rubella syndrome (CRS) can occur in the developing fetus of a pregnant woman infected with rubella virus (RV) in early pregnancy. After a rubella outbreak from early 2012 to late 2013 in Japan, another outbreak re-emerged from mid-2018 in the Tokyo metropolitan area and other large cities. In 2018, and up to epidemiological week (EW) 25 in 2019, more than 4000 rubella cases had been reported. Three CRS cases were also reported up to EW 24. Seroepidemiological surveys among Japanese residents indicated that the susceptible pocket to RV in male adults aged 30-50 years, as determined in 2013, remained unchanged in 2018. To reduce the number of male adults sensitive to RV, in early 2019, Japan's Ministry of Health, Labour and Welfare decided to implement routine immunization of male adults aged 40-57 years between 2019 and 2021. These male adults have been determined to have low anti-RV antibodies, and were therefore designated as the target population for this routine immunization (as category A). Although one-third of male patients with rubella reported in 2018 were in their 20 s and 30 s, these younger generations were not included in the target population for routine immunization against rubella, because they had already received a routine vaccination. Rubella vaccination is also required for male adults aged 20-40 years to diminish the susceptible pocket.
Keywords: epidemiology; rubella; vaccination.