Immunogenicity assay of an experimental inactivated vaccine against bovine parainfluenza virus type 3 in calves

Abstract Background Bovine parainfluenza virus type 3 (BPIV3) is a key pathogen in the bovine respiratory disease complex (BRD). This study aimed to develop an effective inactivated vaccine using an indigenous Iranian BPIV3 strain, evaluating different inactivation methods and adjuvants. Methods The viral antigen was inactivated with either 4 mM binary ethyleneimine (BEI) or 3% hydrogen peroxide (H₂O₂) and then formulated with aluminum-based adjuvants, including aluminum hydroxide [Al(OH)₃], aluminum phosphate [AlPO₄], or a combination of both. Twenty-two calves were randomly divided into a negative control group (saline, n = 1), a positive control group vaccinated with the commercial trivalent vaccine Hiprabovis® 3 ( n = 3), and six experimental vaccine groups ( n = 3 per group). Calves received two subcutaneous injections on days 0 and 21. Serum neutralizing antibody titers were measured by virus neutralization test over a 360-day period following vaccination. Results BEI-inactivated vaccines induced significantly higher neutralizing antibody (NAb) titers than H₂O₂-inactivated or commercial vaccines ( P < 0.05) over most of the study period. H₂O₂-inactivated vaccines also generated a significant NAb response. All aluminum adjuvants yielded acceptable results, with Al(OH)₃ and AlPO₄ showing comparable and better durability than the commercial vaccine. Conclusion Under the conditions of this study, inactivation with BEI was more effective than H₂O₂ in producing vaccines that induced higher levels of neutralizing antibodies against BPIV-3 in calves. Although H₂O₂ has been reported to offer potential advantages in terms of safety and environmental impact, these aspects were not assessed in the current study and deserve further evaluation. Both aluminum hydroxide [Al(OH)₃] and aluminum phosphate [AlPO₄] adjuvants proved suitable for BPIV-3 vaccine formulation, as they elicited robust and durable neutralizing antibody responses.