Effectiveness of emergency vaccination in controlling a foot-and-mouth disease epidemic in a previously FMD-free without vaccination country

Foot-and-mouth disease (FMD) vaccines are key tools for controlling and eradicating FMD virus (FMDV) and are often used as a control measure during epidemics. Emergency vaccination decisions in previously FMD-free countries should be supported by evidence on vaccine effectiveness (VE) against transmission. Mathematical models help assess vaccination strategies but require accurate effectiveness parameters. While experimental studies have shown that FMD vaccination, particularly in cattle, effectively controls transmission, there is limited information on its effectiveness during emergency vaccination in formerly FMD-free countries. We assessed the effectiveness of emergency FMD vaccination implemented alongside other control measures such as ban on animal movements and enhanced biosecurity, estimating VE at one, two-, and three-weeks post-vaccination. VE was estimated by assessing the reduction in the between farm transmission rate parameter () following vaccination of the farms with commercial bivalent vaccines containing the O1 Campos and A24 Cruzeiro strains. To estimate, we prepared the data within an SIR modelling framework and fitted a Generalized Linear Model with a complementary log-log link (cloglog). Since vaccination was implemented by zones during the epidemic, analyses were performed separately for each zone. It was observed that VE increased over time across all vaccination zones. Notably, even within the first week post-vaccination, VE was high, with estimates of 77.65% [70.53-82.94] in zone Pre, 71.05% [21.13-87.59] in zone A, 78.50% [75.44-81.21] in zone B, 68.80% [59.55-75.83] in zone C, and 59.75% [47.68-69.12] in zone D. Evaluating vaccine performance in fully susceptible livestock populations under high-risk conditions is key to improving control strategies and preparedness. Our findings indicate that emergency vaccination, as an additional measure, effectively contributed to control the epidemic in Uruguay. These VE estimates can parameterise and refine outbreak-response models and strengthen preparedness in previously FMD-free regions.