Abstract
Foot-and-mouth disease (FMD) is a highly contagious and economically devastating disease. Traditional intramuscular (IM) injection of inactivated FMD vaccines has been crucial for disease control, but intradermal (ID) immunization offers advantages such as reduced vaccine dosage and decreased animal discomfort. The differences in immune efficiency of intradermal and intramuscular delivery of FMD commercial inactivated vaccine in pigs remain unclear. Here, we compared the immune efficacy of ID and IM immunization using the same dose of commercial FMD vaccine. Experimental pigs were administered the vaccine via either ID or IM routes. At 28 days post-immunization (dpi), the ID group produces less uniform levels of FMDV-specific antibodies than IM groups. The detection of IL-4, IL-6, and IFN-γ in porcine serum samples revealed a lower cellular immune response in the ID group as well in the early stages. Meanwhile, the IM group exhibited higher percentages of CD8(+)T cells producing IFN-γ. These results indicate that, at the same dose of FMDV antigen emulsified with adjuvant ISA 201VG, initial humoral and cellular immune responses were weaker in the ID group compared to the IM group in the early stages, and the uniformity of antibody response levels was poorer in the ID group. While ID immunization holds promise for future vaccine strategies, its application with the current inactivated FMDV vaccine carries a higher risk of immunization failure due to the heterogeneity of immune responses.