Current status of measles in Japan.

Approximately 20,000 to 30,000 cases of measles are reported annually in Japan, although the actual number of measles infections is considered to be five to ten times higher than the number of reported cases. Despite the availability of effective and safe live attenuated vaccines, regional outbreaks in Okinawa, transmission in adults, and secondary vaccine failures continue. Recent advances in molecular technology have contributed to molecular epidemiological studies, new concepts of asymptomatic infection, and the identification of different characteristics among measles virus genotypes.