Efficacy of Ingelvac PRRSandreg; Modified Live Virus Vaccine against Heterologous Porcine Reproductive and Respiratory Syndrome Virus Challenges

Porcine reproductive and respiratory syndrome (PRRS) is an infectious disease caused by the PRRS virus (PRRSV) and characterized by reproductive failure, respiratory disease and weight loss in swine. Two randomized, blinded vaccination-challenge studies evaluated the efficacy of Ingelvac PRRS® modified live virus (MLV) vaccine in protecting pigs from the virulent heterologous PRRSV isolates, restriction fragment length polymorphism (RFLP) 1-3-4 and 1-7-4. In separate challenge studies, pigs were vaccinated on Day 0 with Ingelvac PRRS MLV or placebo ‘challenge control’ and challenged on Day 28 with PRRSV 1-3-4 or 1-7-4. In the 1-3-4 challenge study, pigs vaccinated with Ingelvac PRRS MLV demonstrated significantly lower median viraemia (area-under-the-curve for Day 28–42 [AUC28–42]; P<0.0001) compared with unvaccinated controls. Vaccinated pigs also had significantly higher average daily weight gain (ADWG) than unvaccinated controls (P<0.0001). At Day 42, vaccinated pigs had significantly lower least square mean lung lesion scores than unvaccinated controls (P<0.001). Mortality was significantly higher with challenge control (61%) than with Ingelvac PRRS MLV (15%; P<0.01). In the 1-7-4 challenge study, significantly lower AUC28–42 viraemia levels were observed with Ingelvac PRRS MLV compared with challenge control (P=0.031). Median rectal temperatures were significantly lower with Ingelvac PRRS MLV than with challenge controls at Days 29 and 42 (P<0.01 for both). Pigs vaccinated with Ingelvac PRRS MLV had significantly higher ADWG during the challenge phase (P<0.05) and significantly lower least square mean lung lesion scores at Day 42 compared with unvaccinated controls (P<0.05). These data indicate that Ingelvac PRRS MLV provides heterologous protection against two relatively new and particularly virulent PRRSV field strains responsible for a growing number of infections in the US.