Using a concurrent challenge with porcine circovirus 2 and porcine reproductive and respiratory syndrome virus to compare swine vaccination programs

The objectives of the present study were to evaluate the immune response of six commercial vaccines against PRRSV-2 and PCV2, administered as monovalent or combined products via intramuscular (IM) or intradermal (ID) routes. Seventy-two, 3-week-old pigs were randomly allocated into 8 treatments with 9 pigs each: IMPP0/PCVMH7, IDPP0/PCVMH7, IMING0/PCVMH7, IMPP0/PCVMH0, IDPP0/PCVMH0, IMTRF0, NV/CH, and NV/NC. IMPP0/PCVMH0 and IMPP0/PCVMH7 groups were IM vaccinated once with Prime Pac PRRS (MSD Animal Health, The Netherlands) at 0 days post-vaccination (DPV), followed by single IM vaccination with Porcilis PCV M Hyo (MSD Animal Health, The Netherlands) either at 0 or 7 DPV, respectively. IDPP0/PCVMH0 and IDPP0/PCVMH7 groups were ID vaccinated once with Prime Pac PRRS (MSD Animal Health, The Netherlands) at 0 DPV, followed by a single concurrent ID injection of Porcilis PCV ID (MSD Animal Health, The Netherlands) and Porcilis M Hyo ID ONCE (MSD Animal Health, The Netherlands) either at 0 or 7 DPV, respectively. The IMING0/PCVMH7 group was IM vaccinated once with Ingelvac PRRS MLV (Boehringer Ingelheim, Germany) at 0 DPV, and subsequently IM vaccinated with Ingelvac CircoFLEX (Boehringer Ingelheim, Germany) and Ingelvac MycoFLEX (Boehringer Ingelheim, Germany) at 7 DPV. The IMTRF0 group was IM vaccinated once with combined products of Ingelvac PRRS MLV (Boehringer Ingelheim, Germany), Ingelvac CircoFLEX (Boehringer Ingelheim, Germany), and Ingelvac MycoFLEX (Boehringer Ingelheim, Germany) at 0 DPV. The NV/CH and NV/NC groups were left unvaccinated. At 28 DPV (0 days post-challenge, DPC), pigs were intranasally inoculated with a 4 ml of mixed cell culture inoculum containing HP-PRRSV-2 (105.6 TCID50/ml) and PCV2d (105.0 TCID50/ml). Antibody response, IFN-γ-secreting cells (SC), and IL-10 secretion in supernatants of stimulated PBMC were monitored. Sera were collected and quantified for the PRRSV RNA and PCV2 DNA using qPCR. Three pigs from each group were necropsied at 7 DPC, lung lesions were evaluated. Tissues were collected and performed immunohistochemistry (IHC). Our study demonstrated that concurrent vaccination via the ID or the IM route did not introduce additional reactogenicity. We found no interference with the induction of immune response between vaccination timing. In terms of an immune response, ID vaccination resulted in significantly lower IL-10 levels and higher IFN-γ-SC values compared to the IM-vaccinated groups. In terms of clinical outcomes, only one IM-vaccinated group showed significantly better efficacy when antigens were injected separately compared with concurrently. While the vaccines were ID delivered, these effects disappeared. Our findings confirm that concurrent vaccination of PRRSV-2 MLV and PCV2 via either the IM or the ID routes could be a viable immunization strategy to assist with the control of PRDC. In situations where maximal efficacy is required, over all other factors, concurrent vaccination is possible with the ID route but might not be an ideal strategy if using the IM route.