Field efficacy of a novel porcine reproductive and respiratory syndrome modified-live virus vaccine with an emphasis on growth performance.

Background: This field evaluation was designed to evaluate the efficacy of a new porcine reproductive and respiratory syndrome virus-2 (PRRSV-2) modified live virus vaccine at three independent pig farms.

Methods: Three farms were selected for this study based on their respiratory disease status caused by PRRSV-2 infection in post-weaning and growing pigs. Each farm housed a total of 40, 18-day-old pigs that were randomly allocated to one of two treatment groups. Pigs were administered a 1.0 mL dose of the bivalent vaccine intramuscularly at 21 days of age in accordance with the manufacturer's recommendations, whereas unvaccinated pigs were administered a single dose of phosphate buffered saline at the same age.

Results: Vaccinated groups were measured and calculated significantly (p < 0.05) higher in body weight and average daily weight gain on all three farms compared with unvaccinated groups. Vaccinated groups elicited PRRS antibodies and PRRSV-2-specific interferon-γ secreting cells, which reduced the amount of PRRSV-2 genomic copies in the blood and reduced macroscopic and microscopic lung lesions severity when compared with unvaccinated groups.

Conclusions: The field evaluation data demonstrated that a new PRRSV-2 modified live virus vaccine was efficacious in swine herds suffering from respiratory diseases caused by PRRSV-2 infection.