Vaccines for preventing Japanese encephalitis

Area of Science:

• Public Health
• Immunology
• Infectious Diseases

Background:

• Japanese encephalitis vaccination is crucial but faces challenges like production shortages, cost, licensure issues, and concerns about effectiveness and safety.
• These factors negatively impact vaccination program success and public acceptance in affected regions.

Purpose of the Study:

• To systematically evaluate Japanese encephalitis vaccines based on their effectiveness, safety (adverse events), and immunogenicity.
• This evaluation aims to inform vaccination strategies and address current program limitations.

Main Methods:

• A comprehensive literature search was conducted in March 2007, including major databases (Cochrane, MEDLINE, EMBASE, LILACS, BIOSIS) and contacting authors and manufacturers.
• Included studies were randomized controlled trials (RCTs), including cluster-RCTs, comparing Japanese encephalitis vaccines against placebo, no intervention, or alternative vaccines.
• Data extraction and quality assessment were performed independently, with efficacy calculated as percentage vaccine efficacy based on relative risks and confidence intervals.

Main Results:

• Eight RCTs involving over 358,000 participants evaluated two licensed and three pre-licensure vaccines.
• The licensed inactivated Nakayama vaccine demonstrated 95% efficacy for one year. An unpurified precursor vaccine showed 81% efficacy in year one and 59% in year two.
• Mild to moderate adverse events (soreness, fever, headache) occurred in <6% of inactivated vaccine recipients. The live-attenuated SA14-14-2 vaccine showed similar adverse event rates to controls. Pre-licensure vaccines were immunogenic and relatively safe.

Conclusions:

• Currently, only one of the three widely used Japanese encephalitis vaccines has undergone efficacy assessment via RCT.
• Existing RCTs indicate that current vaccines are generally safe, causing only occasional mild to moderate adverse events.
• Further research is essential to confirm the effectiveness and safety of currently used vaccines, optimize dosing, and evaluate new vaccine candidates.