Comparative safety and efficacy of subcutaneous and intradermal administration of inactivated Japanese encephalitis vaccine during predeployment preparations in the Australian Defence Force.

Japanese encephalitis is a viral disease emerging in areas of influence for the Australian Defence Force immediately north of the continent, including the Torres Strait border of Australia and Papua, New Guinea. Only the mouse brain-derived, inactivated, Nakayama strain vaccine is commercially available to the Australian Defence Force. This vaccine has a high cost and significant adverse event profile, requiring restricted duties after administration. To address these issues, intradermal vaccination (either single intradermal administration or two intradermal injections at two separate sites) was assessed, compared with the conventional subcutaneous vaccination method, in a randomized controlled trial among soldiers preparing for deployment. Dual intradermal vaccination (0.1 mL at two sites) was found to have a slightly more favorable adverse event profile while maintaining comparable serological efficacy and reduced cost. An expansion of the concept and a test of logistics were conducted by vaccinating a battalion formation during predeployment medical preparations. The method of vaccination was well accepted and retained comparable immunogenicity.