To date no commercially available vaccine has succeeded in controlling infections by Piscirickettsia salmonis, the causative agent of SRS. Accordingly there is a need for an effective vaccine against Piscirickettsia salmonis. 
It is an object of the present invention to provide a protein based vaccine or a Nucleic Acid Vaccine (NAV) to protect fish against infection by Piscirickettsia salmonis, and thereby against SRS.