PROBLEM TO BE SOLVED: To provide a technology capable of controlling an infectious disease caused by intracellular parasitic pathogen of fishes by a highly effective vaccine.SOLUTION: An adjuvant for an inactivated vaccine against intracellular parasitic pathogen of fishes, including 1-type interferon or interferon-&gamma； is provided. The adjuvant is especially useful for enhancement of vaccine effect of an inactivated vaccine against Edwardsiella tarda of a flatfish. Further, a vaccine against intracellular parasitic pathogen is also provided, which is obtained by combining inactivated intracellular parasitic pathogen of fishes or a non-infectious antigen of pathogen having vaccine activity, with 1-type interferon or interferon-&gamma；.
