Needle-free intradermal delivery of a recombinant PRRSV-vectored CSFV E2 vaccine enhances humoral immunity and growth performance in piglets.

Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) and Classical Swine Fever Virus (CSFV) remain among the most economically devastating pathogens of swine worldwide. Needle-free intradermal vaccination has emerged as a promising alternative to conventional injection, potentially improving animal welfare, biosecurity, and antigen delivery efficiency within high-density swine production systems. A recombinant PRRSV-vectored live vaccine expressing the CSFV E2 protein (rPRRSV-E2) was evaluated in fifteen 30-day-old healthy piglets. Animals were randomly assigned to three groups: intramuscular injection of rPRRSV-E2 vaccine(needle-based rPRRSV-E2 immunization), intradermal injection of rPRRSV-E2 vaccine (needle-free rPRRSV-E2 immunization), or mock control. Piglets were tracked for clinical signs, growth, and rectal temperature to 63 dpv (Days Post Vaccination). PRRSV/CSFV antibodies were assayed by Enzyme linked immunosorbent assay (ELISA); viral RNA in serum, swabs, and tissues by RT-qPCR. Gross and histopathology were done at 63 dpv. Both vaccination routes induced seroconversion to PRRSV and CSFV by 14 dpv, with the intradermal injection group exhibiting significantly higher antibody level for both antigens (*p < 0.05). No PRRSV RNA was detected in samples from either vaccinated group. Compared to intramuscular injection, intradermal injection significantly improved the average daily weight gain, while causing no fever or notable clinical symptoms, no macroscopic or microscopic lesions, and no differences in gross pathology were noted relative to controls. Intradermal injection of rPRRSV-E2 vaccine elicited robust humoral responses against PRRSV and CSFV, matched pathogen clearance capacity of conventional injection, improved growth performance, and reduced the need for invasive handling. These findings support intradermal injection as a viable, welfare-oriented strategy for integrated control of PRRSV and CSFV in swine herds, with potential application in biosecurity-driven and high-throughput vaccination programs.