Efficacy of a modified-live IBR-BVD-PI3-BRSV-Mannheimia haemolytica toxoid vaccine against challenge with virulent BHV-1 and PI3 viruses in calves 60 days of age
Efficacy of attenuated (att) bovine herpesvirus type 1 (BHV-1) and bovine parainfluenza type-3 (PI3) viruses as antigen fractions in a modified-live virus (MLV) multivalent vaccine was evaluated following single, subcutaneous (SC) administration and intranasal (IN) challenge 28 days after vaccination, with either virulent BHV-1 or PI3 viruses in young calves. A total of 80 seronegative calves, 50 to 63 days of age at the time of vaccination, were used in 2 separate studies with 40 animals per study. Calves were allocated to 2 treatment groups with 20 animals per group which received either a single dose of a MLV IBR-BVD-PI3-BRSV vaccine, Mannheimia haemolytica toxoid, or corresponding placebo formulation without targeted test antigen fractions attBHV-1 (Study 1) or attPI3 (Study 2). Incidence and duration of clinical signs associated with respiratory disease, rectal temperatures, virus shedding, and serologic responses were compared between treatment groups in each study to assess vaccine efficacy. The 5-way vaccine induced significantly higher (p<0.0001) virus neutralizing antibody responses and reduction in fever (p<0.0001), mean rectal temperatures, and lower incidence or shorter duration of clinical disease related to BHV-1 and PI3 infection than placebo-treated calves. Infectious bovine rhinotracheitis (IBR) disease, hallmark of BHV-1 infection, was observed in 95% of control calves and in only 10% of vaccinates. Vaccinated animals in Study 1 and Study 2 demonstrated a 98.8 and 98.9% reduction in virus shedding, respectively, and significantly (p<0.0001) shorter duration of virus shedding compared to control calves, demonstrating protective vaccine efficacy.