The decision on when to administer a booster should be based on the risk of infection. The Strangvac SPC states that in horses at high risk of S. equi it is recommended to repeat the primary regime after 2 months.8 However, in Rendle D et al. 2025 the authors stated that they "do not believe that repeating the primary course after only 2 months is necessary under normal conditions and would only advocate a booster at 3 months if the risk of disease was considered to be very high and would ordinarily be happy to advise boosters at 6–12-month intervals according to risk. If the level of risk increases, then the interval can be decreased so vaccination with Strangvac effectively constitutes a responsive disease management intervention."3
Multiple strangles dangers threaten your clients1,2
If not identified and treated, strangles can spread rapidly with severe consequences for the entire yard1,2
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S. equi is among the most frequently occuring infectious diseases of horses, and can lead to serious complications, such as respiratory distress and guttural pouch empyema.1-3 Strangles represents up to 28% of equine respiratory disease cases,4 with a mortality rate of up to 10%.2,5
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The operational dangers of strangles can soon take their toll through extra vet and staffing costs, biosecurity measures (such as fencing, PPE, disinfectant), disruptions to service and attendance of events, and loss of income while the yard is closed.4,6
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The financial dangers of strangles can rapidly add up.1,5,7 One study from 2016, reported that the average monthly cost incurred during an outbreak was £7,814 a month, including stocks and supplies, staff time, blood sampling and transportation.7
Why choose Strangvac
Strangvac is a revolutionary vaccine against strangles, a highly contagious respiratory disease3,5,6,8
An innovative approach to strangles
Strangvac is the gold standard when strangles closes in3,5,6,8
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With over 80,000 doses administered to date, Strangvac has been tried and tested across Europe, including extensive use around the UK.8,9
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Strangvac targets eight specific, highly conserved antigens. And because these antigen sequences remain consistent globally, the vaccine is highly effective against all known strains of the bacteria.6,8,10
If you are interested in hearing more about how well conserved the Strangvac antigens are across isolates of Strep. equi, please visit Dechra Academy, where you will find a recording of Dr. Frosth’s presentation from IEIDC congress 2021.11
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When tested in a clinical trial, 15 of 16 ponies vaccinated with Strangvac against strangles demonstrated protection. In this trial, the horses were given a dose of strangles 10,000x the minimum dose required to infect the lymph nodes of ponies.6
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Strangvac contains no live bacteria or proteins associated with development of severe forms of the disease (e.g. SeM proteins).3,8 This means it has negligible risk of causing strangles or severe forms of the disease, such as purpura haemorrhagica.3,8
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Strangvac is designed around innovative recombinant fusion protein technology, rather than live bacteria, and so contains no bacterial DNA.8 A vaccinated horse, therefore, will not trigger a positive test.5,8
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With Strangvac, the most common adverse events are injection site reactions and fever, both of which are mild and transient. The majority of adverse events resolve without the need for veterinary care.3
The Strangvac vaccination schedule3
When to vaccinate with Strangvac
We recommend that horses should be vaccinated when strangles is:3
Strangvac has a simple, flexible vaccination schedule3
Strangvac is administered as two doses given 4 weeks apart. You can then expect the horse to have full immunity 2 weeks after the second dose.8 To maintain immune protection, a booster can then be given 12 months after the second dose.3,13
How do we decide when a booster is required? add
What if the risk of strangles changes? add
With Strangvac, the frequency of revaccination can be increased or decreased to suit the yard’s situation. So, if a yard close by has a strangles outbreak, you can administer a booster earlier than planned.3,6,14
Can a horse have Strangvac at the same time as the flu vaccine? add
No information is available on the safety and efficacy of this vaccine when used with any other veterinary medicinal product. A decision to use this vaccine before or after any other veterinary medicinal product therefore needs to be made on a case by case basis.8
Performing a risk assessment can help you decide when to administer boosters3,14
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
Keep an eye on strangles outbreaks in your area
Strangles may be closer than you think15
The UK has seen a 25% increase in strangles cases in the first half of 2026 compared with the same period in 202515*
Region: Whole of the UK
Date range: 12/05/25 - 11/05/26
Total strangles diagnoses: 532
Total number of affected regions: 75
In the UK, the Surveillance of Equine Strangles (SES) network provides up to date information about strangles outbreaks. You can use their website to monitor if there are any outbreaks across the UK, including in your veterinary practice’s location. You can also sign up for emails on outbreaks.15
*1st January 2025 to 31 May 2025 = 202 strangles cases; 1st January 2026 to 31 May 2026 = 260 strangles cases.15
Act fast and vaccinate before strangles closes in.3,5
Faced with strangles, act fast and act on the signs3,5
Read more
If strangles is suspected, divide horses into three isolation groups as per the traffic light system.3
Read more
Vaccinate horses with no clinical signs to reduce the spread and severity of disease.3
Read more
Minimise contact with people and equipment to reduce transmission. Educate owners on the need to isolate new horses – the majority of outbreaks occur due to a new horse, that is already infected, being introduced to a yard.5
Read more
Check temperatures twice a day for a minimum of 3 weeks. Horses showing clinical signs or pyrexia during this period should be moved to the red group.3
As fever is the first clinical sign of infection with strangles, and shedding of bacteria typically begins 24-48 hours later, there is time to act with biosecurity measures and vaccination before strangles spreads.16
Implement the traffic light system when strangles is a danger3
If strangles is suspected, divide horses into three isolation groups as per the traffic light system.3
Read more
For horses in the green group that have not been exposed to strangles, Strangvac can be administered to healthy horses to provide protection from the spread of the disease.3
If one or more of these horses comes into contact with a horse with strangles, they should be moved to the amber group. If one of these horses develops clinical signs of strangles, they should be moved to the red group.3
Read more
Horses in the amber group should be vaccinated, if they show no clinical signs of strangles after a period of monitoring. If they develop a fever or other signs of the disease, they should be moved to the red group.3
Read more
Horses in the red group have shown clinical signs of strangles. They should not be vaccinated until they have recovered. Give these horses supportive care until they have fully recovered, which can take several weeks.3
It is important not to reintroduce a horse to the rest of the yard until you are sure the disease is no longer present.3
When strangles closes in, Strangvac is proven to help mitigate the danger1,5
Access publications showing how Strangvac has been used as part of biosecurity measures.
Vaccination is not a replacement for isolation protocols. It serves as a vital adjunct to minimise the severity of any cross-contamination with a horse infected with strangles.5
When horse owners are at risk of strangles, they want their vets to tell them17
Horse owners consider their equine vets to be their most trusted source of health information17
Encourage owners to vaccinate before it's too late
Access horse owner and vet resources
We recognise that vets play an important role in helping horse owners protect their yards against strangles. We have therefore created a number of resources for vets, to help them educate owners. This includes a Practice Tool Kit, which can be downloaded below.
Strangvac Digital Brochure
Biosecurity Infographic
Strangles Practice Toolkit
Vaccination Schedule
Horse Owner Website
FAQs
Which horses can be vaccinated? add
The vaccine is licensed for use in horses from the age of five months.8 Vaccination against strangles 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
- 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
- Horses kept in yards with poor biosecurity
The safety of Strangvac has not yet been tested in pregnant mares and breeding stallions.8 Therefore, due to limited data, the decision to use Strangvac in pregnant mares is at the attending vet’s discretion, based on a risk-benefit assessment, with informed consent from the owner.8
Can I combine Strangvac with other vaccines? add
No information is available on the safety and efficacy of this vaccine when used with any other veterinary medicinal product.8
The vaccine should be used only according to the benefit-risk assessment by the responsible veterinarian. A decision to use this vaccine before or after any other veterinary medicinal product therefore needs to be made on a case-by-case basis.9 If you would like further advice, please contact our Technical Team here.
Should I vaccinate in an outbreak situation? add
As stated on the Strangvac SPC, you should only vaccinate healthy animals. The same applies during an outbreak.8
If strangles is suspected, one published study (Rendle et al. 2025) recommends dividing horses into three isolation groups as per the traffic light system:3
- Horses in the green group have not been exposed to strangles. Strangvac can be administered to provide protection from the spread of the disease.
- Vaccinated horses that have not been in contact with cases:
- Administer booster 2/3 months after the second vaccination and then every 6 months to maintain immunological memory3
- Unvaccinated horses
- Start primary course: partial protection from two weeks after second dose. Serum antibody concentrations increase within 7 days6
- Vaccinated horses that have not been in contact with cases:
- Horses in the amber group have had either direct or indirect contact with infected (red group) horses within the last three weeks. It is sensible to monitor the amber group, taking temperatures twice daily, for 10-14 days. Begin vaccinating if no fever/clinical signs are seen
- Horses in the red group show clinical signs of strangles. Horses with clinical signs should NOT be vaccinated. We would advise that clinical cases in a 'red' group should not be vaccinated until 3 months after recovery
It is worth also noting the following:
- Horses who have previously received a primary course of Strangvac vaccine are likely to be better protected should there be an outbreak. These horses will also have a further increase in clinical protection in response to a booster vaccination. One study (Robinson et al. 2020) demonstrated that immunological memory is retained for at least 12 months after only the primary course. However, immunity was enhanced by administration of a booster 3 months after the second vaccination of the primary course.6
- Rendle et al. 2025 advocate for a booster at 3 months if the risk of disease is considered to be high (e.g. in an outbreak).3 Otherwise, we recommend a booster every 12 months.3,13
There is additional published data available to support use in a strangles outbreak situation:
- Rendle D, et al. Strangles vaccination: A current European perspective. Equine Vet Educ 2025;37:90–97.
- Gröndahl G 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 2026; 58(2): 476–485.
- Rask E, et al. Closing the Stable Door on Strangles: Serological Responses of Vaccinated Horses on a Farm Following the Arrival of a New Horse. Animals (Basel) 2025;15(24):3584.
Should I vaccinate young, old or non-competition horses? add
Strangles can affect horses of all ages.2 Due to the high morbidity, and the risk of mortality,1,2,5 all horses may benefit from vaccination with Strangvac.1,3,5,8
- If a horse always remains on a yard, it is still at risk of strangles if other horses come and go3
- Young horses seem to exhibit more severe clinical signs if they become infected with Strep. equi2
Vaccination has been shown to reduce the clinical signs and the number of abscesses in these susceptible horses.8
Can a vaccinated horse become infected? add
No vaccine can claim 100% protection.18 Vaccinated horses can still be infected and shed Strep. equi.8
If a vaccinated horses does become infected, Strangvac has been demonstrated to reduce clinical signs of disease in the acute stage of the infection with Strep. equi.8 This includes reductions in:8
- Number of abscesses within submandibular and retropharyngeal lymph nodes
- Body temperature increases
- Coughing
- Inappetence
- Difficulty swallowing
- Changes in demeanour
How to administer and store Strangvac? add
Administer one dose (2 ml) by intramuscular injection, followed by a second dose (2 ml) four weeks later.8
- The neck and gluteals are recommended over the pectorals, due to the risk of larger injection site swellings in the pectorals8
- Store and transport refrigerated (2ºC to 8ºC)8
- Do not freeze8
- Keep the vial in the outer carton to protect it from light8
Keen to learn more about strangles and vaccination?
Please visit Dechra Academy for a series of interesting presentations on the subjects.
Strangles’ diagnosis, control and vaccination by Andrew Waller.
Conservation of antigen sequences across a global population of Strep. equi by Sara Frosth.
Functional activities of antibody responses following vaccination of ponies with a multicomponent subunit vaccine against strangles by Francesco Righetti.
Click here to view the comprehensive module with all three presentations
References add
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Gröndahl G, et al. Equine Vet J. 2026;58:476–485.
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Boyle et al. J Vet Intern Med. 2018;32:633–647.
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Rendle D, et al. Equine Vet Educ 2025;37:90–97.
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National Equine Health Survey (NEHS) 2018. Available at: https://www.bluecross.org.uk/sites/default/files/d8/2022-01/NEHS-results-2018.pdf (Accessed June 2026).
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Rask E, et al. Animals (Basel). 2025;15(24):3584.
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Robinson C, et al. Vaccine. 2020;38(31):4861–4868.
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Redwings. Redwings Strangles Survey Results: Main report 2017. https://www.redwings.org.uk/sites/default/files/2023-09/Strangles%20survey%20results%20main%20report%202017%20FINAL%20small_0_0.pdf (Accessed June 2026).
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Strangvac SPC.
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Strangvac unit sales Aug 22 – May 26.
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Frosth S, et al. Equine Vet J. 2022;55:92-101.
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Frosth S, et al. Conservation of antigen sequences across a global population of S. equi. Presented at 11th International Equine Infectious Diseases Conference 27th September–1st October 2021.
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Your Horse. Available at: https://www.yourhorse.co.uk/news/livery-yard-strangles-vaccination-policy/ (Accessed June 2026).
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Paillot R, et al. Vaccines. 2026;14(6):533.
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Ivens, P. Available at: https://www.vettimes.co.uk/app/uploads/wp-post-to-pdf-enhanced-cache/1/implementing-biosecurity-in-an-equine-environment.pdf (Accessed June 2026).
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Surveillance of Equine Strangles (SES). Available at: https://www.equinesurveillance.org/ses/ (Accessed June 2026).
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British Horse Society. Available at: https://www.bhs.org.uk/horse-care-and-welfare/health-care-management/horse-health/equine-diseases/strangles/ (Accessed June 2026).
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Strangles horse owner survey, May 2025.
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World Health Organisation. Available at: https://www.who.int/news-room/feature-stories/detail/vaccine-efficacy-effectiveness-and-protection (Accessed June 2026).