Objective—To determine whether an inactivated
bovine respiratory syncytial virus (BRSV) vaccine
would protect calves from infection with virulent
Design—Randomized controlled trial.
Animals—27 nine-week-old calves seronegative for
Procedure—Group-1 calves (n = 9) were not vaccinated.
Group-2 calves (n = 9) were vaccinated on days
0 and 21 with an inactivated BRSV vaccine containing
a minimum immunizing dose of antigen. Group-3
calves (n = 9) were vaccinated on days 0 and 21 with
an inactivated BRSV vaccine containing an amount of
antigen similar to that in a commercial vaccine. All
calves were challenged with virulent BRSV on day 42.
Clinical signs and immune responses were monitored
for 8 days after challenge. Calves were euthanatized
on day 50, and lungs were examined for lesions.
Results—Vaccination elicited increases in BRSV-specific
IgG and virus neutralizing antibody titers and in
production of interferon-γ. Virus neutralizing antibody
titers were consistently less than IgG titers.
Challenge with BRSV resulted in severe respiratory
tract disease and extensive pulmonary lesions in control
calves, whereas vaccinated calves had less
severe signs of clinical disease and less extensive pulmonary
lesions. The percentage of vaccinated calves
that shed virus in nasal secretions was significantly
lower than the percentage of control calves that did,
and peak viral titer was lower for vaccinated than for
Conclusions and Clinical Relevance—Results suggest
that the inactivated BRSV vaccine provided clinical
protection from experimental infection with virulent
virus and decreased the severity of pulmonary
lesions. Efficacy was similar to that reported for modified-live BRSV vaccines. (J Am Vet Med Assoc 2001;218:1973–1980)