Robust cross-immunity against a heterologous field strain of foot-and-mouth disease virus achieved in small ruminants following commercial vaccination in Jordan.

INTRODUCTION: Foot-and-mouth disease (FMD) is a contagious infectious disease, with a severe socio-economic impact, affecting cloven-hoofed livestock. Routine and emergency vaccinations are the most effective tool for the containment and the eradication of the disease in endemic countries. Due to the presence of the virus in seven serotypes and in various lineages and strains, the selection of the most appropriate vaccine is essential to achieve protection. According to WOAH/FAO guidelines, assessing vaccine effectiveness is recommended to improve control strategies. This study reports the analysis of the results from Post Vaccination Monitoring (PVM) performed in Jordan across 2022 and 2023. METHODS: A polyvalent inactivated vaccine, including one strain serotype O (O/EURO-SA/O1/Campos) and two strains serotype A (A/EURO-SA/A24/Cruzeiro and A/ARG/2001), was administered to naïve small ruminants (goats and sheep). About one half of the animals received a second dose 28 days after the first. Antibody titres were determined by Virus Neutralisation Test (VNT) against two FMD serotype O strains: one closely related to the vaccine strain and the other that had recently circulated in the country. RESULTS: Overall, a single administration of the vaccine was effective in inducing a good response in small ruminants, but a second administration boosted immunity, increasing the level and duration of the immune response in almost all vaccinated animals. The same vaccinal response was apparent when measured against the field strain. DISCUSSION: This field study corroborated the results of vaccine matching and confirmed the current suitability of that particular vaccine formula in the containment of FMD in the Middle East area.