Concurrent vaccinations against PCV2 and PRRSV: study on the specific immunity and clinical protection in naturally infected pigs

The present study aims at evaluating the efficacy of the concurrent PCV2 and PRRS vaccinations in comparison with single vaccinations and placebo in pigs exposed to both natural viral infections. Four groups of pigs (200 animals each) at 4 weeks of age were considered. Pigs from group A were concurrently vaccinated with a modified live PRRSV-1-based vaccine and a genotype a-based PCV2 subunit (Cap) vaccine via the intramuscular route. Animals from groups B and C were vaccinated with PRRSV and PCV2 vaccines alone, respectively, and group D was inoculated with the adjuvant alone. Clinical score (morbidity), mortality and average daily weight gain (ADWG) were evaluated. Viremia, virus-specific ELISA antibodies and cell-mediated immunity (CMI) as IFN-γ secreting cells by ELISpot were detected. The clinical signs associated with PRRSV infection lasted from 8 to 16 weeks while those related to PCV2 infection from 5 months of age. The results showed that the concurrent vaccinations reduced clinical signs and increased the preventive fraction (40.4%) and the ADWG. In concurrently vaccinated pigs, the probability of dying due to infection, especially in association with PCV2 viremia was reduced 3-fold. PRRSV viremia was not reduced by vaccination but lower and shorter PCV2 viral load was detected in both concurrently and single PCV2-vaccinated pigs. Despite the presence of maternally-derived antibodies, animals showed a prompt seroconversion after vaccination and PCV2 natural infection. Moreover, maternal immunity did not interfere with the development of the specific cellular IFN-γ SC response in single and concurrently vaccinated animals. The study demonstrates that concurrent PRRSV + PCV2 vaccination has no interference with the development of the specific humoral and cell-mediated immunity and it is associated with clinical protection upon natural challenge.