The Evaluation of a Porcine Circovirus Type 2 (PCV2) Intradermal Vaccine Against a PCV2 Field Strain

<b>Background/Objectives:</b> Porcine circovirus type 2 (PCV2) has a major impact on swine productivity. Vaccines are used to aid in control and mitigate production losses. We investigated the protection provided by an intradermal PCV2 vaccine against a field strain in Taiwan. <b>Methods:</b> We conducted a safety and efficacy study. In the safety study, four Specific Pathogen Free (SPF) piglets were enrolled in the study. One was selected as the control and left unvaccinated, one was selected to be intradermally vaccinated with five times the standard dose (1 mL, Porcilis^® PCV ID), and the other two were vaccinated with two times the standard dose (0.4 mL, Porcilis^® PCV ID). All animals were observed for 3 weeks for adverse events post-vaccination. In the efficacy study, twelve SPF pigs negative for the PCV2 antibody were randomly divided into two groups. The first group of six pigs was vaccinated (Porcilis PCV ID, 0.2 mL) intradermally at 3 weeks of age. The second group of six pigs was sham vaccinated with 0.2 mL of normal saline. At 7 weeks of age, all pigs were challenged with the PCV2 strain CYC08 (1 × 10⁵ TCID₅₀/mL) by nasal and intramuscular injection. Clinical monitoring of body temperature and mortality was conducted daily. At 11 weeks of age, all animals were sacrificed for histopathological analysis. <b>Results:</b> No adverse events were reported in the safety study. In the efficacy study, the vaccinated animals had statistically improved results in the following areas post-challenge: body temperature rise, viremia, virus shedding, mortality, tissue histopathological and microscopic scores. <b>Conclusions:</b> The study results support that a one-dose PCV2 vaccine administered intradermally with a needle-free injector is safe and provides protection when challenged with a field PCV2 strain.