If a vaccine with DIVA capability is used, then the horse will only test positive if it has been infected with strangles previously, not because it has been vaccinated.2,8
Given the serious impact a strangles outbreak has on horse welfare and yard finances, preventing the infection from spreading is vital.1,2 Biosecurity and vaccination go hand-in-hand as the two most important steps you can take to limit the spread when new horses enter your yard.2,3
Choose an option to find out more
Why vaccinate against strangles?
When to vaccinate against strangles
Vaccination is highly recommended for:3
•
Any horses that frequently travel or mix with others and/or livery yards with mixed ownership,
particularly if there are frequent new arrivals
particularly if there are frequent new arrivals
•
Premises with regular visiting horses or horses transiting through
•
Studs that accept walk-in mares and the mares that visit them
•
Equestrian businesses where an outbreak would threaten their commercial viability or have
an unacceptable impact
an unacceptable impact
•
Horses kept in yards with poor biosecurity
•
Horses on a yard where there has been an outbreak nearby
Perform a risk assessment
The aim of a risk assessment is to clearly identify what concerns and disease transmission risks exist for your horses and the yard as a whole.5 You should discuss any risk assessment with your vet, so you can decide what biosecurity measures need to be in place and when, as well as whether to vaccinate.5 Below is an example of a recommended risk assessment.
Click a column to view the risk level
Risk assessment result
| Single horse | Multiple horses | Multiple horses + owners |
Large yard; livery yard | |
|---|---|---|---|---|
| Contact with other horses |
None | Occasional, known health status | Regular, known health status | Frequent, unknown health status |
| Arrivals | None | Unusual | Several times a year | Frequent, high throughput |
| Previous strangles |
None | None | Previous, but investigated | Previous, no investigations |
| Quarantine | Annual / preventative health plans in place | Quarantine new arrivals with testing | Quarantine new arrivals no testing | No quarantine or testing |
| Water troughs | Separate | Separate / Communal | Separate / Communal | Communal |
| Personnel traffic |
None, biosecurity in place | Little, biosecurity in place | Yes, biosecurity in place | Yes, no biosecurity |
Single horse: Low Risk
Contact with other horses
None
Arrivals
None
Previous strangles
None
Quarantine
Annual / preventative health plans in place
Water troughs
Separate
Personnel traffic
None, biosecurity in place
Multiple horses: Medium Risk
Contact with other horses
Occasional, known health status
Arrivals
Unusual
Previous strangles
None
Quarantine
Quarantine new arrivals with testing
Water troughs
Separate / Communal
Personnel traffic
Little, biosecurity in place
Multiple horses + owners: High Risk
Contact with other horses
Regular, known health status
Arrivals
Several times a year
Previous strangles
Previous, but investigated
Quarantine
Quarantine new arrivals no testing
Water troughs
Separate / Communal
Personnel traffic
Yes, biosecurity in place
Large yard; livery yard:
Highest Risk
Contact with other horses
Frequent, unknown health status
Arrivals
Frequent, high throughput
Previous strangles
Previous, no investigations
Quarantine
No quarantine or testing
Water troughs
Communal
Personnel traffic
Yes, no biosecurity
Strict biosecurity measures and vaccination are important ways to reduce the risk of a strangles outbreak on your yard2,3
FAQs – Your questions answered
Will my horse test positive for strangles because it has been vaccinated? add
What is DIVA and why is it important? add
DIVA is short for: Differentiate Infected from Vaccinated Animals.9
A revolutionary intramuscular strangles vaccine has become available that does not contain live or killed S. equi cells.7 Instead, this vaccine targets the equine immune response to eight important proteins.3,8 These proteins are different to those used in the diagnostic blood test for exposure to strangles.3,8 Horses vaccinated with a DIVA vaccine can attend events and sales, or move yards normally without triggering positive tests, unless they have been exposed to strangles.3
Will I still be able to ride/compete my horse immediately after vaccination? add
Most horses are back in full work by 3 days post-vaccination.10 This also depends on whether the horse shows a rise in body temperature as a reaction to vaccination or not. A transient increase in body temperature after vaccination is not uncommon as this is part of the immune system activation.7
References add
-
Boyle et al. J Vet Intern Med. 2018;32:633–647.
-
Rask E, et al. Animals (Basel). 2025;15(24):3584.
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Rendle D, et al. Equine Vet Educ 2025;37:90–97.
-
McGlennon A. et al. Equine Vet J. 2025; 58(2): 533-548. doi: 10.1111/evj.14558.
-
Ivens, P. Vet Times. Available at: https://www.vettimes.co.uk/app/uploads/wp-post-to-pdf-enhanced-cache/1/implementing-biosecurity-in-an-equine-environment.pdf (Accessed July 2026).
-
Your Horse. Available at: https://www.yourhorse.co.uk/news/livery-yard-strangles-vaccination-policy/ (Accessed July 2026).
-
Strangvac SPC.
-
Robinson C, et al. Vaccine. 2020;38(31):4861–4868.
-
Pasik J, et al. Anim Health Res Rev 2004;5(2):257-62.
-
Hedenström U, et al. Equine Veterinary Education 2026:38(8):e544-e549.
-
British Horse Society. Available at: https://www.bhs.org.uk/horse-care-and-welfare/health-care-management/horse-health/equine-diseases/strangles/ (Accessed July 2026).