Evaluation of a DIVA compliant trivalent negative marker vaccine for foot-and-mouth disease in cattle.

Foot-and-Mouth Disease (FMD) continues to pose a major threat to global livestock health and food security, particularly in endemic regions like India. A primary challenge in FMD control is the inability of conventional vaccines to differentiate infected from vaccinated animals (DIVA), a limitation that complicates surveillance and restricts international trade. To address this, we evaluated a trivalent negative-marker FMD vaccine targeting serotypes O, A, and Asia 1, with immunogenicity and protective efficacy assessed in cattle, the target host species. The vaccine elicited robust humoral and cellular immune responses. Virus-neutralizing antibody titers peaked at 2-4 weeks and remained significant for six months. Cellular profiling revealed a dynamic Th1/Th2 response, characterized by an early IL-4 peak at 7 days post-vaccination (DPV), followed by peak IFN-γ secretion at 14 DPV, correlating with antibody isotype switching from IgG1 to IgG2, indicating a balanced immune response. Importantly, the vaccine conferred protection of cattle against homologous serotype O virus challenge for up to six months. Furthermore, DIVA compliance was unequivocally demonstrated by the absence of antibodies to the deleted 3A segment in repeated booster vaccination studies in guinea pigs. Collectively, these findings show that the trivalent marker vaccine provides protective efficacy equivalent to conventional vaccine while enabling the immunological monitoring essential for strategic FMD control programs.