Varicella vaccine: the Japanese experience.

Varicella vaccine developed by the Biken Institute (Osaka, Japan) was administered to 1.39 million subjects in Japan and 1.93 million in Korea between 1987 and 1993. Six years after licensure, it was assessed for safety and efficacy under the regulatory requirements of the Japanese government. Clinical symptoms were reported in 6.9% (580/8429) of vaccines (mostly healthy children) and seroconversion in 91.5% (2347/2565), and the mean antibody titer 1 month after immunization was 12.2. Despite 100 well-documented contacts with varicella patients, only 2 (2%) developed breakthrough varicella with very mild clinical features within 12 months of vaccination. Immunologic tests in 26 recipients showed presence of humoral and cellular immunities to varicella-zoster virus (VZV) for > or = 20 years. These data indicate that this live attenuated varicella vaccine provides long-term protective immunity against VZV infection.