Duration of immunity of a quadrivalent vaccine against respiratory diseases caused by BHV-1, PI3V, BVDV, and BRSV in experimentally infected calves

Several laboratory studies assessed the duration of immunity of a quadrivalent vaccine (Rispoval?4, Pfizer Animal Health) against bovine respiratory diseases (BRD) caused by bovine herpes-virus type-1 (BHV-1), parainfluenza type-3 virus (PI₃V), bovine viral-diarrhoea virus type 1 (BVDV), or bovine respiratory syncytial virus (BRSV). Calves between 7 weeks and 6 months of age were allocated to treatment and then were injected with two doses of either the vaccine or the placebo 3 weeks apart. Six to 12 months after the second injection, animals were challenged with BHV-1 (n = 16), PI₃V (n = 31), BVDV (n = 16), or BRSV (n = 20) and the course of viral infection was monitored by serological, haematological (in the BVDV study only), clinical, and virological means for ≥2 weeks. Infection induced mild clinical signs of respiratory disease and elevated rectal temperature in both vaccinated and control animals and was followed by a dramatic rise in neutralising antibodies in all treatment groups. Titres reached higher levels in vaccinated calves than in control calves after challenge with BHV-1, BVDV, or BRSV. On day 3 after PI₃V challenge, virus shedding was reduced from 3.64 log₁₀ TCID₅₀ in control animals to 2.59 log₁₀ TCID₅₀ in vaccinated animals. On days 6 and 8 after BRSV challenge, there were fewer vaccinated animals (n = 2/10 and 0/10, respectively) shedding the virus than control animals (n = 8/10 and 3/10, respectively). Moreover, after challenge, the mean duration of virus shedding was reduced from 3.8 days in control animals to 1 day in vaccinated animals in the BVDV study and from 3.4 days in control animals to 1.2 days in vaccinated animals in the BRSV study. The duration of immunity of ≥6 months for PI₃V, BHV-1 and BVDV, and 12 months for BRSV, after vaccination with Rispoval?4, was associated mainly with enhanced post-challenge antibody response to all four viruses and reduction of the amount or duration of virus shedding or both.