News Notes

Experimental Vaccine Protects Against Strangles During Outbreak

By Modern Equine Vet News Staff

Horses vaccinated with an experimental vaccine during a strangles outbreak remained healthy, suggesting the vaccine was protective, a recent study found.

During this real-world study, 17 healthy horses were vaccinated with Strangvac (Intervet and Dechra) 23 days after Streptococcus equi subspecies equi was confirmed in 3 unvaccinated horses that lived on the same farm. This was considered day 0. The researchers took serum samples on day 0, day 28 and day 489 and measured total antibody titers with iELISA. They also measured specific antibody concentrations to S. equi using the antigen A/C iELISA, which can differentiate between infected and vaccinated animals.

In addition, the researchers monitored the horses for clinical signs of disease.

The found that the horses began developing increased antibodies almost immediately and continued to develop antibodies to day 28. None of the vaccinated horses developed strangles, but 5 of the 7 of the original vaccinated horses tested seropositive with the A/C iELISA on day 489, which was 377 days after their third vaccination.

“Despite adherence to recommended biosecurity measures, serological evidence of exposure to S. equi was demonstrated in half of the vaccinated horses. Notably, all horses vaccinated during the outbreak responded to the vaccine components and remained healthy, suggesting a protective effect of vaccination of healthy horses with Strangvac in outbreak situations,” the researchers wrote.

The vaccine is not yet approved for use in the United States, but Intervet and Dechra initiated safety studies in December. The safety trials will include approximately 600 horses across 4 states, in accordance with the Department of Agriculture regulations. The company intends to start efficacy studies during the second half of 2026. MeV