title: Duration of immunity to experimental infection with bovine respiratory syncytial virus following intranasal vaccination of young passively immune calves.
abstract: OBJECTIVE
  To determine whether a combination modified-live bovine respiratory syncytial virus (BRSV) vaccine could stimulate protective immunity in young BRSV-seropositive calves following intranasal administration and determine the duration of clinical immunity.
  
  
  METHODS
  Controlled challenge study. Animals-84 dairy calves (3 to 11 days old).
  
  
  METHODS
  Responses to BRSV challenge of seronegative calves vaccinated under licensing trial conditions were compared with those of seropositive calves 2 times after vaccination. In experiment 1, young BRSV-seronegative calves were vaccinated intranasally with a minimum immunizing dose of BRSV and challenged with BRSV approximately 7 weeks later. In experiments 2 and 3, young BRSV-seropositive calves were vaccinated intranasally with a commercially available combination modified-live virus vaccine containing the commercial dose of the BRSV fraction and challenged with BRSV 9 weeks or approximately 14 weeks later, respectively.
  
  
  RESULTS
  In experiments 1 and 2, BRSV-vaccinated calves had significantly higher Pao2, significantly fewer lung lesions, and significantly lower mortality rate than did unvaccinated calves subsequent to BRSV challenge. In contrast, in experiment 3, there were no differences in Pao2, lung lesions, or mortality rate between vaccinated and control calves after BRSV challenge approximately 14 weeks after vaccination. Protected calves in experiment 1 consistently had significant anamnestic mucosal and systemic antibody responses after challenge, whereas in experiments 2 and 3, antibody responses after challenge were more variable.
  
  
  CONCLUSIONS
  A combination BRSV vaccine administered intranasally to young calves induced protective immunity in the presence of maternal antibodies. The duration of immune responses induced by intranasal vaccination was short (≤ 4 months). Boosting immunity iatrogenically, or by natural exposure, is probably required to obtain optimal responses to neonatal intranasal vaccination.
authors.affiliation: Departments of Veterinary Microbiology, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, SK S7N 5B4, Canada.
authors.forename: John A
authors.initials: JA
authors.lastname: Ellis
authors.forename: Sheryl P
authors.initials: SP
authors.lastname: Gow
authors.forename: Suman
authors.initials: S
authors.lastname: Mahan
authors.forename: Randy
authors.initials: R
authors.lastname: Leyh
mesh_terms: D000818:Animals; D000914:Antibodies, Viral / Q000097:blood; D002417:Cattle; D002418:Cattle Diseases / Q000097:blood / Q000517:prevention & control* / Q000821:virology; D007112:Immunity, Maternally-Acquired; D007070:Immunoglobulin A / Q000097:blood; D007074:Immunoglobulin G / Q000097:blood; D018357:Respiratory Syncytial Virus Infections / Q000097:blood / Q000517:prevention & control / Q000662:veterinary* / Q000821:virology; D018112:Respiratory Syncytial Virus, Bovine / Q000276:immunology*; D017201:Virus Shedding
chemical_list: D000914:Antibodies, Viral; D007070:Immunoglobulin A; D007074:Immunoglobulin G