[A live attenuated varicella vaccine].

The vaccine virus was isolated from a vesicle of a 3-year-old otherwise healthy boy called Oka (his family name) who had typical varicella. This virus was passaged through human embryonic lung cells, guinea pig embryonic cells at a low temperature, and human diploid cells (WI-38). It was then adapted to MRC-5 human diploid cells for vaccine preparation. The vaccine contains cell-free virus with a minimum of 1000 plaque forming units per dose and suitable stabilizers. In 1974 the vaccine was administered to hospitalized children immediately after the occurrence of an index varicella case because preventive methods, such as administration of VZV immune globulin, were unavailable at the time. The vaccine prevented the spread of varicella throughout the children's ward of the hospital. Subsequently, the vaccine was shown to be immunogenic, well tolerated, and efficacious even in high-risk children. The vaccine has been studied extensively with largely favorable results. The vaccine was initially licensed in Japan in 1987 for high-risk children but was extended just after licensure to include normal children based on the needs of parents and physicians. Because varicella vaccination is not compulsory in Japan, only approximately 40% of Japanese children received the vaccine in 2008. This low level of coverage was not sufficient to alter the circulation of wild-type VZV, and the epidemiology of natural varicella has not changed since the vaccine was introduced. The most dramatic changes were reported in the USA after the introduction of a universal immunization strategy in 1996, causing vaccine coverage to increase to 89% in 2006. As a result, there have been substantial declines among both children and adults in the incidence of varicella, hospitalizations and ambulatory visits for varicella, mortality due to varicella, varicella-related complications, and overall expenditures for varicella-related illnesses. The vaccine is now commercially available worldwide and was administered to approximately 16 million individuals in approximately 80 countries in 2006. The universal immunization strategy should be introduced in Japan as soon as possible.