VP1 Genetic Characterization, Antigenic Profiling, and Cross-Protection Analysis of Foot-and-Mouth Disease Virus Serotype O Isolates Circulating in Vietnam During 2019–2024

Foot-and-mouth-disease (FMD) is a highly contagious disease affecting cloven-hoofed animals, with important direct and indirect socio-economic impacts on the livestock industry. Although the disease has been successfully eradicated from some regions, it is still endemic in most of the world. One of the main tools for its prevention is the use of vaccines that contain strains that match antigenically with the FMD strains circulating in the field, together with a good epidemiology plan. Additionally, the characterization of circulating strains is useful to maintain antigen banks updated to be prepared to deal with eventual disease outbreaks. Previous studies have reported genetic changes in the evolution of FMD virus type O circulating lineages in Vietnam and other countries of Southeast Asia. Here, we present genetic and antigenic characterization of type O viral strains circulating in Vietnam during 2019 until 2024. Vaccine matching tests were performed using a sera pool collected from pigs vaccinated with a monovalent vaccine containing the O1 Campos strain at 28 days post-vaccination. High neutralizing antibody titers were recorded for type O isolates, with r1 values over 0.3 in most of the cases, indicating good cross-reactivity. Furthermore, a swine challenge test performed against one of the field isolates from the Mya-98 lineage exhibited 100% protection even with a single vaccine dose. Together, these results support the potential of high-potency O1 Campos vaccines to provide clinical protection against antigenically and genetically distinct FMD virus serotype O strains circulating in endemic regions.