New Study Demonstrates One Year Duration of Immunity for Strangvac® Vaccination

A new study 1 demonstrates at least one year duration of immunity for the strangles vaccine, Strangvac®, providing further evidence that booster vaccinations can be given at yearly intervals and integrated into an annual vet check-up.

This correlates with another study published this year that found that antibody responses in sports horses were equivalent, whether revaccinated with Strangvac at five or 12 months after their second dose 2 , following natural exposure to Streptococcus equi (S. equi).

The new study was a retrospective analysis of six independent double-blinded placebo-controlled experimental infection studies involving 129 ponies (80 vaccinated controls and 49 placebo controls) and a serology study (12 vaccinated ponies). The ponies received two to five vaccine doses before being challenged with highly infectious experimental doses of S. equi strain Se4047; ponies in the serology study were not experimentally infected.

All the unvaccinated horses developed pyrexia , however vaccinated ponies showed significantly delayed pyrexia, with 46.25% reaching the end of the study with none at all. The antibody titres to all three antigens (CCE, Eq85, IdeE) demonstrated robust protection of 78.9% to 81.2% in vaccinated animals one year after the second dose of Strangvac and were estimated to continue to provide significant protection. These findings support the observed levels of protection by Strangvac against natural infection with S. equi.

Mary Battersby, veterinary surgeon and equine veterinary advisor at Dechra, the company behind the Strangvac vaccine, comments: “The new study provides further evidence that annual Strangvac boosters offer significant protection against strangles and can be integrated into annual vet check-ups to encourage uptake. Recent studies 3, 4 have also demonstrated Strangvac’s protective effect during outbreak situations.”

For further information on the Strangvac vaccine visit www.dechra.co.uk or contact your local Dechra territory manager.

References
1. Paillot R., Righetti F., Robinson C., Frykberg L., Flock M., Zachrisson O., Guss B., Flock J-I., Waller A. Antibody titres to Strangvac antigens correlate with protection and duration of immunity against experimental infection with Streptococcus equi Subspecies equi. Vaccines 2026, 14, 533

2. Hedenström U., Righetti F. 2, Zahl I., Henriques-Normark B., Gustafsson A., Hartman E., Paillot R., Ruiz A., Waller A. Serological responses of Sport horses pre- and post-third vaccination with Strangvac. Equine Veterinary Education, January 2026; 00:1–6.

3. Rask, Erika et al. “Closing the Stable Door on Strangles: Serological Responses of Vaccinated Horses on a Farm Following the Arrival of a New Horse.” Animals : an open access journal from MDPI vol. 15,24 3584. 13 Dec. 2025, doi:10.3390/ani15243584 https: pubmed.ncbi.nlm.nih.gov/41463869/

4. Gröndahl G, Righetti F, Aspán A, Bjerketorp J, Frosth S, Frykberg L, et al. Reining in strangles: absence of disease in horses vaccinated with a DIVA-compatible recombinant fusion protein vaccine, Strangvac, following natural exposure to Streptococcus equi subspecies equi. Equine Vet J. 2025. https://doi.org/10.1111/evj.70125

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