Abstract: The present invention relates to a live avirulent infectious pancreatic necrosis virus which has been shown to be genetically stable in biological studies. Fish exposed to said virus turn out positive for the virus without showing any signs of disease and the avirulent virus has also been shown to protect the fish against IPN for an extended period of time after administration. Thus, a vaccine comprising said virus and said virus for the prophylaxis or treatment of infectious pancreatic necrosis disease are also part of the present invention.