The vaccine formulation and its role in inflammatory processes in fish--effects and adverse effects

Adjuvants are helper substances that assist in the development of vaccine efficacy by enhancing the magnitude, extending the duration and/or directing the nature of the immune response. Most fish vaccines for injection are formulated with oil adjuvants and provide a strong and long-lasting immunity. Inherent problems of such formulations are the injection-site reactions, the challenge being to balance adjuvanticity against reactogenicity to produce a sufficient level of protection with as few side-effects as possible. Current findings on cellular inflammatory responses to oil adjuvanted vaccines in fish and on prediction factors for the effect versus side-effect balance are being discussed. The focus of future vaccine formulation studies will probably comprise the effect of formulation parameters on antigen retention, and the effect of antigen purity and concentration on recipient fish responses at the cellular and cytokine level.