[Background of recent JE vaccine issues]

Area of Science:

• Epidemiology
• Immunology
• Public Health Policy

Context:

• Japanese encephalitis (JE) virus remains prevalent in Japan, despite a significant decrease in reported cases since 1992.
• JE immunization was a routine childhood vaccination in Japan until 2005.
• Concerns regarding adverse events, specifically acute disseminated encephalomyelitis (ADEM), following JE vaccination emerged.

Purpose:

• To review the background and reasons behind the Ministry of Health, Labor and Welfare's (MOHLW) 2005 decisions regarding JE immunization in Japan.
• To analyze the shift in JE vaccine policy, including the discontinuation of routine immunization recommendations and the consideration of alternative vaccine types.

Summary:

• The MOHLW ceased recommending JE immunization as a routine childhood vaccination in May 2005, citing concerns over medical costs for ADEM cases, recognized as adverse events.
• The ministry also discontinued the fifth dose of JE vaccine for adolescents in July 2005, considering the current epidemiological situation and immunization status.
• A shift towards a Vero cell-derived JE vaccine was anticipated to mitigate potential neurological adverse events associated with the current mouse brain-derived vaccine.

Impact:

• These policy changes reflect a complex interplay between vaccine safety, public health, and evolving scientific evidence.
• The decisions highlight the challenges in balancing disease prevention with the management of vaccine-related adverse events.
• The review provides insights into the decision-making process for national immunization programs in response to safety and efficacy concerns.