Equine flu, as equine influenza is commonly known, is caused by various strains of the influenza virus that affect the upper and lower respiratory tract of horses, donkeys and mules. It is a major and economically important cause of acute respiratory disease throughout the world, with the exception of some island nations, such as Iceland and New Zealand. As H&H’s veterinary advisor Karen Coumbe has said, “equine flu rarely kills horses, but it does kill horse events”.
There has been a significant increase in cases of equine flu in the British horse population since 1 April 2026. This has led to tighter biosecurity requirements at horse shows and other places where horses come together. Six-monthly vaccinations are being recommended with horses’ passports now being checked on arrival at many venues. The increase in cases is not inline with the normal pattern, which research published in the Equine Veterinary Journal has shown typically increases in the final quarter of the calendar year.
British Equestrian (BEF) is calling for “horse owners, yard managers and vets to adopt a risk-based approach when moving horses, particularly between premises, events and regions” during this outbreak. The BEF has also stated that France is also seeing heightened equine influenza activity, particularly in the north of the country, so advises using “extreme caution when travelling horses to, from or through there”. This also applies to purchasing horses from France.
- View the latest data from the Equine Infectious Disease Surveillance website
Equine flu: Signs | How it spreads | Is it serious? | Diagnosis | Treatment | Prevention | Vaccine schedule | During an outbreak
What are the signs of equine flu?
- A very high temperature of 39-41C (103-106F) which lasts for one to three days
- A frequent harsh, dry cough that can last for several weeks
- A clear, watery nasal discharge that may become thick and yellow or green
- Enlarged glands under the lower jaw
- Clear discharge from the eyes and redness around eyes
- Depression and loss of appetite
- Sometimes filling of the lower limbs, muscle stiffness and other signs such as weight loss
How do horses catch equine flu?
As with the human version, equine flu is very contagious. With an incubation period of one to five days, it spreads rapidly as the virus is released into the atmosphere by infected animals. It is mainly acquired through inhalation of virus from ill animals coughing and spluttering infected respiratory droplets. Indirect spread is also possible via buckets or grooms/handlers/nurses/vets.
Unlike strangles and some other infections, the flu virus does not linger nor survive for long outside the horse, but it can be airborne, blowing over surprisingly long distances, certainly more than 1km.
Once the virus has been inhaled, it invades the lining (epithelium) of the horse’s airway, which becomes inflamed, producing a very sore throat and a nasty cough. This damage causes patches of the membranes lining the airways to ulcerate, which disrupts the clearance of mucus and debris from the airways causing a thick discharge from the horse’s nose. Bacteria then invade the damaged areas leading to further infections.
How serious is equine flu: do I need to call the vet?
If your horse shows a raised temperature and/or any signs of equine influenza, strict hygiene and isolation procedures should be adhered to immediately and you should contact your vet.
Horses that have been in contact with an affected animal should be carefully monitored and should not attend shows or external clinics or training.
It is recommended that horses on a stable yard with an outbreak of equine flu do not leave the premises while the outbreak is ongoing.
Diagnosis of equine flu
An accurate diagnosis of equine flu can be made by:
- recognising the clinical signs and the history of rapid spread between horses
- isolation of the virus through nasal or nasopharyngeal swabs
- rising antibody levels in blood (serum) samples taken early in the course of the disease and two to three weeks later
- history of recent contact with a confirmed case of the disease
Vaccinated horses may still show signs, but these are usually much milder than those seen in unvaccinated horses.
Equine flu treatment
Basic nursing is key when treating a horse with the virus. Good stable ventilation and dust-free management is essential. Exposure to dust should be minimised, as horses with respiratory infections are more susceptible to airway irritation. It is best to switch to dust-free bedding and feed soaked hay, or better still haylage, from the floor.
If weather permits and risks to other animals are manageable, then affected horses benefit from being turned out for at least part of the day once their temperatures have returned to normal. This is especially important in the recovery stages. At the same time infected horses should be isolated.
Antibiotics have no effect against a virus, but can be useful to control secondary bacterial invasion. This is a risk in foals or elderly or otherwise unwell animals, which can succumb to fatal pneumonia. Medications to help breathing can prove beneficial.
How long does equine flu last?
Horses that catch equine flu typically start to show signs around one to five days after exposure and it may take three to six weeks before the signs pass, assuming they are receive appropriate care.
Horses with a respiratory infection should be given complete rest and not restart any strenuous exercise until at least three to four weeks after the signs have gone.
How to prevent flu in horses
Flu is difficult to control, especially in equine that are frequently transported and mixed extensively, so regular vaccination of horses is important. Equine flu outbreaks are most common when young susceptible horses are brought together at sales and shows, or for weaning and training.
Surprisingly low numbers of the UK’s horse population are vaccinated, despite the fact that vaccination is the preferred method of control and is compulsory when competing under British Horseracing Authority, FEI and affiliated governing bodies’ rules in the UK.
Whenever you attend shows or training outings away from home, you should follow strict biosecurity and hygiene methods such as:
- Do not allow horses to touch or sniff other horses
- Riders/grooms should only handle their own horses and tack
- Do not share buckets or kit with other horses/riders
- Avoid using on-site water facilities. If this is impossible, avoid placing the hose into the bucket and sanitise your hands before carrying the bucket to the horse
- Avoid hand grazing your horse at a venue
- Ensure show stables have been disinfected before and after use and all bedding removed and replaced with fresh
- Horse’s temperature should be taken before travel to an external venue
- Horses returning from external venues should be isolated if possible, with their temperature and their health closely monitored
How often are horses vaccinated for flu?
All British equine sport governing bodies require the minimum of the first two vaccines to have been given prior to attending competition.
The British Horseracing Authority introduced new flu vaccination rules on 1 January 2022 to harmonise with other racing authorities in Europe. The new rules increased the frequency of boosters from 12 months to six months and reduced the time periods between the first and second vaccines from 21-92 days to 21-60 days, and between the second and third vaccines from 150-215 days to 120-180 days.
NB: We recommend all competition riders double check the latest version of the appropriate rulebook to ensure your horse’s vaccinations comply with their governing body’s requirements.
British Horseracing Authority: horses must have been vaccinated against equine flu within the past six months. Horses must not have been vaccinated less than seven days before racing.
FEI competitions: a booster vaccination must have been given no more than six months and 21 days prior to competing. A vaccination should not have been given within seven days of the competition or of entry into the FEI stables.
British Dressage (BD): Once a horse has received its first three vaccinations, further vaccinations can be given at 12 monthly intervals, but not within seven days of competing. In response to the spring 2026 outbreaks, BD is “strongly recommending that all members move to a six-month vaccination cycle”. If your horse’s last vaccination was more than six months ago, BD recommends “that you bring their annual booster forward to provide sufficient cover when competing during the summer season”.
British Eventing (BE): Horses require an annual booster every 12 months for national BE competitions, since 1 January 2026. A horse may not compete if it has been given the booster on any of the seven days before it is to compete at an event. Although six monthly boosters are not mandated by BE, the organisation strongly advises that horse owners and competitors give horses an additional booster at this time of high risk if they were last vaccinated more than six months previously.
British Showjumping (BS): Horses to have received booster vaccinations not more than 365 days from their last vaccination, and should not compete within seven days of receiving a vaccination. In response to the spring 2026 outbreaks, BS venues will be carrying out passport checks on arrival. BS has shared the Equine Infectious Disease Action Group’s recommendation that owners whose horses were last vaccinated more than six months ago, are strongly recommended to bring their next booster forwards to give them the best protection during the outbreak.
British Riding Clubs (BRC): Horses must have had their initial course, plus annual (12 month) vaccinations to attend BRC qualifiers and/or championships.
If a horse or pony is competing in one discipline for instance, showjumping but it is attending an event at a venue, such as a racecourse, it will be required to comply with the vaccination requirements under the rules of racing, which means it must have been vaccinated within six month, but not in the previous seven days.
The British Horseracing Authority has stated that, from Wednesday 20 May 2026, only horses from licensed training yards will be allowed to enter racecourses on racedays. This means all scheduled hunter chases from 20 May have been called off and Retraining of Racehorses (RoR) parades are cancelled. Racecourses are also increasing the period of time between hosting an equine event involving horses from unlicensed premises and a licensed raceday to six clear days (from three).
The vaccination record(s) in the horse’s passport, must be completed, signed and stamped line by line, by an appropriate veterinary surgeon (who is neither the owner nor the rider of the horse). The responsibility to comply with this rule lies with the owner, who should consult with their vet.
From 1 January 2026, for horses competing under FEI rules, flu vaccinations must be recorded digitally in the FEI HorseApp, as well as in the horse’s passport. Vets must enter the vaccination details on the day it is administered. There is a transition period running until 30 June 2026 during which no sanctions will be issued, but from 1 July 2026 missing or incorrect digital records may result in fines for the person responsible (this is usually the horse’s rider).
What to do during an equine flu outbreak?
If flu occurs locally, it may be advisable to give a booster vaccination to any healthy horse that has not been vaccinated in the previous six months. Consult your vet for advice.
The BEF explains that “frequent boosters ensure antibody levels remain high, which is essential for reducing both the severity of the disease and risk of the virus shedding within the wider equine population”.
You may wish to limit the situations where you expose your horse to others by reducing the competitions and training outings you attend, or choose only to visit venues that actively check the vaccination status of equines in attendance and require six-monthly boosters.
Can humans catch equine flu?
The equine influenza virus is similar to the flu virus that affects people, but is not identical, so horses cannot catch human influenza or vice versa.
References and further reading
What happened after the epidemic? Equine influenza surveillance sheds light on sources and seasonal risk in the United Kingdom Equine Veterinary Journal, 5 March 2026
British Dressage’s equine influenza update, British Dressage website, 20 May 2026
British Showjumping’s equine influenza update, British Showjumping website, 21 May 2026
British Eventing’s equine influenza update, British Eventing website, 21 May 2026
Call for increased vigilance as number of reported equine influenza outbreaks in UK continues to rise, British Equestrian website, 12 May 2026
Annual booster vaccination and the risk of equine influenza to Thoroughbred racehorses Equine veterinary journal, 21 November 2019
British Horseracing Authority: amendments to the vaccines code, October 2021
British Riding Clubs Important Flu Vaccination Update, 21 October 2022
British Eventing vaccination update, British Eventing Facebook page, 15 December 2025
Mandatory registration of equine influenza vaccination details in the FEI HorseApp, FEI website, 12 Dec 2025
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