Evaluation of an Effective Intradermal Foot-and-Mouth Disease Vaccine for Early Protection

<b>Background:</b> In South Korea, foot-and-mouth disease (FMD), a highly contagious viral infection that affects cloven-hoofed animals, has led to the implementation of a bivalent FMD vaccination program. The current FMD vaccination strategy involves intramuscular (IM) administration to the shoulder region of the swine. However, this method is associated with adverse reactions at injection sites. Our previous studies have demonstrated that intradermal (ID) vaccination eliminates these side effects while maintaining immunogenicity comparable to that of IM vaccination. This study aimed to assess the early immune response induced by ID vaccination and compare its protective ability against FMDV serotype O with that of a commercial IM vaccine recently used in South Korea. <b>Methods:</b> An ID FMD vaccine was evaluated using two adjuvants, ISA 207 (50%) and EMULSIGEN-D (15%). Virus neutralization (VN) titers and structural protein levels were measured to compare efficacy across groups. To assess the early protective efficacy of ID vaccination, viral challenge experiments were conducted at 7 and 14 days post-vaccination (dpv). <b>Results:</b> Swine vaccinated via the ID route exhibited no clinical symptoms at 14 dpv, indicating effective early protection against FMD (O/AS/SKR/2019). In addition, no side effects of FMD ID vaccination were observed. <b>Conclusions:</b> These results suggest that ID vaccination could serve as a viable alternative to conventional IM vaccination, which is frequently associated with adverse effects. Importantly, this study demonstrates that ID vaccination can provide effective early protection within 7-14 days post-vaccination, highlighting its potential utility for emergency outbreak control.