Assessing the comparative longitudinal immunogenicity of two commercial foot-and-mouth disease vaccines in crossbred dairy calves in Sebeta Hawas, Ethiopia

Foot-and-mouth disease (FMD) poses a significant threat to livestock production in East Africa, with serotypes O, A, SAT 1, and SAT 2 persistently circulating in Ethiopia. The objective of this study was to evaluate field-level vaccine performance and compare the seroconversion kinetics of two distinct multi-serotype inactivated formulations among crossbred dairy calves in Sebeta Hawas. To achieve this, a longitudinal trial was conducted comparing a quadrivalent formulation (Vaccine 1; n = 58 calves; containing serotypes O, A, SAT 1, and SAT 2) against a trivalent formulation (Vaccine 2; n = 57 calves; containing serotypes O, A, and SAT 2). Humoral responsiveness was monitored using a solid-phase competitive ELISA (SPCE) over a 168-day post-vaccination period. To account for repeated measures, antibody reactivity profiles over time were analyzed using a Linear Mixed-Effects Model (LMM), complemented by area under the curve (AUC) summation to evaluate total integrated longitudinal percent inhibition kinetics. AUC analysis demonstrated a highly significant main effect of serotype (F(3,396) = 14.32, p < 0.0001), However, neither the main effect of vaccine type (F(1,396) = 1.33, p = 0.250) nor its interaction with the shared serotypes (F(2,396) = 0.063, p = 0.939) on AUC was statistically significant, suggesting comparable total cumulative antibody profiles globally between the formulations. Vaccine 1 maintained significantly higher estimated marginal means at specific time points (e.g., Day 56) for shared serotypes including O ( p < 0.0001), A ( p = 0.0292), and SAT 2 ( p = 0.0203), while additionally providing an independent, robust response against SAT 1. Notwithstanding these short-term kinetic advantages, both vaccines exhibited significant waning of Serotype A antibody reactivity by 168 days post-vaccination, highlighting that FMD seroconversion profiles are context-dependent and vary by serotype and duration. The quadrivalent vaccine (Vaccine 1) is the preferred choice for FMD control in Ethiopia, providing essential broader coverage via its SAT 1 component despite waning Serotype A immunity. Strategic multivalent deployment remains vital, with future work required to optimize booster strategies.