Epidemiology of rubella and congenital rubella infection in Japan.

During the last two decades, the Japanese mainland experienced three rubella epidemics; the first occurred in the latter half of 1960, the second in 1975-1977, and the third in 1981-1982. A retrospective study done after the first outbreak identified 49 newborns with congenital rubella syndrome (CRS). In contrast, the Ryukyu Islands were swept by a rubella epidemic in 1964-1965, and 408 babies with CRS were born, giving an incidence of 20 per 1,000 births. When the 1975-1977 epidemic hit the mainland, a notification system had been established, and two million cases of rubella were reported. In a retrospective survey, only 39 babies with CRS were found. The number of babies with CRS on the mainland was fewer than that observed on the Ryukyu Islands, and clinical illness appeared milder for these two populations than had previously been experienced. These observations seem to support a hypothesis that the teratogenicity of circulating rubella virus is lower in Japan than in the United States.