A single vaccination with an inactivated bovine respiratory syncytial virus vaccine primes the cellular immune response in calves with maternal antibody

As expected the single vaccination did not have any effect on the decline of BRSV-specific neutralising or ELISA antibody. The cellular immune system was however primed by the vaccination. In the vaccinated group virus excretion with nasal discharge was reduced, less virus could be re-isolated from lung tissues and the lungs were less affected.These results indicate that a single vaccination with an inactivated BRSV vaccine was able to break through the maternal immunity and induce partial protection in very young calves. It can be speculated that the level and duration of protection will improve after the second dose of vaccine is administered. A two-dose basic vaccination schedule is recommended under field conditions.The bovine respiratory syncytial virus (BRSV) has been established as an important viral component in the bovine respiratory disease complex (BRDC) [1]. The virus can act synergistically with other viruses such as the bovine parainfluenza type 3 virus (PI3) or bacteria such as Mannheimia haemolytica (Mh), Pasteurella multocida, Haemophilus somnus and Mycoplasma bovis to cause pneumonia [2]. BRSV also fulfils the Koch's postulates to be recognised as an aetiological agent of pneumonia in calves. Respiratory disease is however often milder under laboratory conditions than under field conditions [3-6].Outbreaks of BRSV associated pneumonia typically recur every year [7] and most farms are affected. The mechanisms for the persistence of the virus in a farm are not well understood [8]. Based on sequence divergence among BRSV isolated during recurrent outbreaks in closed herds, (re)introduction of the virus into the herd prior to each new outbreak is the most likely explanation [9]. Airborne transmission of BRSV has been demonstrated under experimental conditions [10].Different approaches have been followed to develop safe and efficacious BRSV vaccines including inactivated vaccines [11,12], (genetically) modified live vaccines [11,13], subunit vaccines [1