Infectious pancreatic necrosis virus (IPNV), belonging to the genus Aquabirnavirus within the family Birnaviridae, causes huge economic loss to the global salmonid industry every year. Recently, outbreaks of disease caused by genogroup I IPNV were found in many rainbow trout (Oncorhynchus mykiss) farms worldwide. An inactivated vaccine was prepared using a genogroup I IPNV isolate with an optimized procedure as incubation with β-propanolactone (BPL) at the final concentration of 0.5% at room temperature for 48 h. The inactivated vaccine was used to immunize rainbow trout, and the protection efficiency was evaluated by viral loads determination, immune-related genes quantification, and neutralizing antibody tests. The viral loads in immunized rainbow trout were significantly decreased and the strongest antiviral effect was observed on 30 days post-immunization (d.p.i). The expression of innate immune-related genes IFN-1, and Mx-1 genes were significantly up-regulated on 3, 7, and 15 d.p.i (p < 0.05), and adaptive immune-related genes CD4, CD8, and IgM genes were significantly up-regulated on 15 and 30 d.p.i (p