[Background of recent JE vaccine issues].

In Japan, more than 5,000 patients were reported in 1950, and there have been less than 10 cases annually since 1992. However, Japanese encephalitis virus caused of Japanese encephalitis (JE) are still existed highly and widely in the country, reported by National Institute of Infectious Diseases with serological examination among domestic pig population. JE immunization had been provided to children as category 1 routine immunization in Japan. However, the Ministry of Health, Labor and Welfare (HOHLW) decided not to recommend JE immunization to children as a routine immunization at May 2005. Major reason on this decision was that the Minter of MOHLW certified to pay loss of medical costs for the case of ADEM (acute disseminated encephalomyelopathy) after JE immunization, recognized as adverse events with JE vaccine, although MOHLW stated that the strict scientific evidence was unknown. MOHLW stated also that it is expected Vero cell derived JE vaccine should be replaced with the present mouse brain derived JE vaccine as the next generation, to be able to avoid theoretical possibility of neurological adverse events associated with JE vaccine. Small but increasing number of requests recently to be certified as health injuries on ADEM cases associated with JE immunization is also another reason for MOHLLW's decision. Further, fifth doses of JE vaccine given to children at 14-15 years old as a routine immunization was decided to be discontinued by MOHLW at July 2005, considering present epidemiological situation on JE and JE immunization status in Japan, although four doses has been recommended continuously as routine. The background details on JE vaccine issues decided by MOHLW in 2005 were reviewed on this paper.