Strangles vaccination

Many horse owners will be aware that a vaccine against Streptococcus equi equi, the bacterium that causes strangles, called Strangvac, became available in 2022. We now have the benefit of three years’ experience of its use in about 10,000 horses throughout Europe, along with a scientific review published in the Equine Veterinary Journal in 2024.

Key points:

• The vaccine is very safe: about 5 per cent of horses experienced heat, pain or swelling at the vaccination site - in the muscle, similar to influenza and tetanus vaccines - which either resolved by itself or with anti-inflammatory medications, such as Bute. Only very rarely were other adverse reactions reported. The vaccine does not inject live bacteria into the horse, so strangles cannot occur as a result of vaccination
• The vaccine is effective at reducing the clinical signs of strangles: as with flu or Covid-19 vaccines, the disease is not eliminated in all cases, but horses are much less likely to show signs of illness and signs are less severe. Crucially, the rate of abscesses developing is vastly reduced, which in turn means that horses are much less likely to become carriers of disease
• The vaccine also helps to protect other horses that your horse contacts: vaccinated horses shed less bacteria so are a lower disease risk to other horses that they meet, at home or away. For this reason, the overall risk of a strangles outbreak at a yard is minimised if all horses at the yard are vaccinated, but there is still benefit to vaccinating only one horse
• Vaccinated horses can be differentiated from horses which have developed antibodies as a result of disease: this means that the blood test that is commonly used to screen horses for recent exposure to Streptococcus equi equi can be used in vaccinated horses. It will also not interfere with guttural pouch scope results
• Vaccination should be used alongside other biosecurity measures: vaccination is not a panacea. An isolation period of 2-3 weeks for new horses entering a yard is advisable, especially when coming from high-risk situations such as dealer yards or group transport. While the blood test for antibodies has its place, recent evidence has shown that it does not reliably detect long-term carriers of disease. Some yards have the policy of carrying out the more accurate guttural pouch scope but because this is invasive and expensive, most do not. Therefore, vaccination of a whole yard could be a useful adjunct to, or even replacement for, blood tests
• Vaccination is cost-effective: when compared with the cost of an outbreak, which is estimated by insurance companies to be about £1000 per clinical case. While some strangles cases are mild and uneventful, full-blown strangles is very unpleasant for the affected horses and can lead to serious long-term sequelae and, rarely, death. An outbreak at a commercial yard usually has significant negative financial consequences, so risk mitigation with vaccination is worth considering
• Safety in pregnant mares has not been fully established: anecdotally, the vaccine appears to be safe for pregnant mares, but this is based on unpublished data, so the risks and benefits should be discussed in each case.

Which horses should be vaccinated?

In theory, if all horses were vaccinated, it might be possible to eventually eradicate strangles. However, this is unrealistic, and efforts should be concentrated to vaccinate horses at medium to high risk:

• Horses at livery yards with movement on and off the yard
• Horses travelling to training, competition or stud
• Horses which are thought to have contacted a clinical case.

What is the vaccine schedule?

A primary course of two injections about a month apart are given. Horses must be healthy at the time of vaccination.

The original data sheet recommends a booster vaccination at 2 months in high-risk situations. However, antibodies are known to last for at least 12 months. A pragmatic approach has been adopted throughout the UK and Europe with boosters being given every 6-12 months, following the initial course, the frequency depending on risk assessment by vet and owner. Should the horse be exposed to a known case, immediate revaccination will maximise protection. Booster vaccinations which run over by more than one month should be restarted, as data demonstrating immune memory beyond the 12-month period is lacking.

The vaccine is not licensed to be given alongside other vaccines, but extensive anecdotal evidence has shown no increase in adverse events if given at the same time as flu or tetanus vaccines, making it a practical option. 

What is the cost?

The cost of the vaccination, as of April 2025, is £60.20, plus any applicable visit fees.

Dechra, the pharmaceutical company which manufactures Strangvac, has launched a scheme to support owners and vets with the costs of the primary course. The initial vaccination will be charged as usual and the second vaccination will be free. The first vaccine must be given in May 2025 to qualify.

Questions?

Please contact the practice and speak with one of our vets if you would like to discuss your individual situation.

Click here to read the full review paper that was published in 2024