Serological responses of Sport horses pre‐ and post‐third vaccination with Strangvac

Summary Background Strangles, caused by Streptococcus equi , is an endemic disease of horses throughout the world. A vaccine against strangles, Strangvac, is available in Europe, but there are no published serological data following the revaccination of Sport horses. Objectives To measure the antibody response of Sport horses to the components of Strangvac before and after third vaccination. Study Design Longitudinal cohort study. Methods Adult Sport horses were administered their third vaccination with Strangvac at 5 months (group 1, n = 20) or 12 months (group 2, n = 15) after second vaccination. Horses were monitored closely for adverse signs. Blood samples were collected from both groups immediately before and 14 days after third vaccination to quantify antibody responses by ELISA. Results Transient signs of mild injection site swelling in 8.5% horses for 2 days, and a temperature rise of ~0.8°C in most horses for 1 day, occurred post‐vaccination. Health status returned to normal within 48 h. The antibody titres to the vaccine components were 3.34 ± 0.31 and 3.14 ± 0.29 before third vaccination and increased significantly to 3.90 ± 0.29 and 3.90 ± 0.17 after third vaccination in groups 1 and 2, respectively ( p < 0.0001 for both groups). Main Limitations Data and samples from a matched unvaccinated control group, or prior to, and 14 days after first and second vaccination were unavailable. Conclusions Strangvac was safe and antibody responses that were generated to the vaccine components after revaccination of Sport horses at 5 or 12 months post‐second vaccination were equivalent.