Vaccination of Atlantic salmon with recombinant VP2 of infectious pancreatic necrosis virus (IPNV), added to a multivalent vaccine, suppresses viral replication following IPNV challenge

Atlantic salmon (Salmo salar) pre-smolts vaccinated with Norvax®Protect (NP) or injected with saline, were demonstrated to have a significantly (P≤0·0001) higher probability of being IPNV-infected when sampled during 12 weeks post challenge (PC) with IPNV (11·7 times and 32·5 times higher, respectively), than fish vaccinated with Norvax®Protect-IPN (NP-IPN), a vaccine identical to NP except for the presence of recombinant VP2. Furthermore, following experimental challenge with IPNV, an IPNV-specific secondary humoral immune response was detected in the group vaccinated with NP-IPN. Statistical analysis revealed that NP-IPN-vaccinated fish had a significantly (P≤0·0001) higher probability of producing IPNV-specific antibodies during 12 weeks PC with IPNV, compared to NP-vaccinated or saline-injected fish (5·3 times and 7·6 times higher, respectively). The results support efficacy data from field trials in Norway, where NP-IPN has proven successful in the prevention of IPN in Atlantic salmon post-smolts. However, the immunological mechanisms behind the increased IPNV clearance remain unknown.