Efficacy of a combination modified-live IBR-BVD-PI3-BRSV vaccine + Mannheimia haemolytica toxoid against challenge with virulent BVDV-1b and BVDV-2 viruses in young calves 60 days of age
Efficacy of attenuated (att) bovine viral diarrhea virus (types 1 and 2) as antigen fractions in a modified-live multivalent vaccine were evaluated following single, subcutaneous (SC) administration and intranasal (IN) challenge 35 to 38 d after vaccination, with either virulent BVDV-1b (Study 1) or BVDV-2 (Study 2) viruses in young calves. A total of 80 BVDV-seronegative Holstein calves, 53 to 61 d of age at the time of vaccination, were used in 2 separate studies with 40 animals per study. In each study, calves were allocated to 1 of 2 treatment groups (20 animals per group) which received either a single dose of combination modified-live bovine rhinotracheitis (BHV-1)-bovine virus diarrhea-parainfluenza 3-respiratory syncytial virus vaccine + Mannheimia haemolytica toxoid, or corresponding placebo formulation without targeted test antigen fractions attBVDV-1a and attBVDV-2. In the respective studies, multivalent vaccine induced significantly higher virus neutralizing antibody responses and reduced incidence and duration of leukopenia and viremia in vaccinated animals compared to placebo-treated animals. Post-challenge leukopenia, a hallmark of BVDV infection, was observed in 75% and 100% of control calves compared to only 26.3% and 25% in vaccinated animals in Study 1 and Study 2, respectively (p=0.006; p=0.0001). In addition, duration of leukopenia was significantly shorter in vaccinates compared to placebo controls (p=0.0091 Study 1; p<0.0001 Study 2). Furthermore, 100% of placebo-treated calves in both studies were viremic compared to 57.9% (Study 1) and 25% (Study 2) of vaccinated animals, resulting in significant reduction of post-challenge viremia (p=0.0012, Study 1; p=0.0001, Study 2). The duration of viremia was significantly shorter (p<0.0001) in vaccinated groups compared to control calves in both studies. In conclusion, data from the current studies demonstrated vaccine efficacy in 60-day-old calves against BVDV-1b and BVDV-2 infection.