17/06/2026
EQUINE INFLUENZA OUTBREAK. WHAT YOU NEED TO KNOW
With the ongoing flu outbreak in the UK and recent confirmed cases in Aberdeenshire and Fife, it’s good to be up to date on the best way to protect your horses.
To do this, let’s look at how flu is spread and how immunity works.Influenza is a viral infection and is highly contagious, spreading via the aerosol route as well as direct contact. In the 2007 outbreak in Australia, it spread up to 5km on the wind without any direct horse-to-horse contact. In one case we were previously involved in, all unvaccinated horses on the yard showed signs within a few days—including those in distant fields. Even if your horses don’t go out anywhere, they can still potentially get infected.
Influenza presents dramatically in unvaccinated horses with a very high temperature, a harsh dry cough, dullness, and lethargy. While it is usually self-limiting with recovery in 10 to 14 days, horses are highly susceptible to secondary infections. In the 2007 Australian outbreak, a surprisingly high mortality rate of up to 5% (1 in 20) was reported in certain high-risk unvaccinated groups (and 1% across all groups). It’s not a disease we can ignore.
So, how best to protect our horses?
All ages of unvaccinated horses are susceptible. With foals, vaccinating too early results in poor lifelong immunity because of the interference of maternally derived antibodies. For this reason, foals should not be vaccinated before six months of age, but for optimum protection, they should be started on their programmes then. At Dykehead, we vaccinate pregnant mares and give a booster around 4 weeks pre-foaling to maximize these antibodies.
Older horses are well protected with modern vaccines incorporating Florida clade 1 strains. Be aware there is one vaccine still used in the UK that hasn’t updated its viral strains for over 20 years and does not provide the same level of protection.
What is the best vaccination schedule?
Once horses have had their initial 2 doses, they will have reasonable immunity within 14–28 days after the second injection. Horses should not compete or do very strenuous work for at least a week after vaccination to allow the immune system to respond optimally without added physical stress.If individual horses are vaccinated every 12 months after the initial primary vaccination course (3 vaccinations), there is good evidence that they will be protected against severe clinical disease. However, generally, immunity drops from around six months post-vaccination. Current evidence suggests that if exposed after this point, although not showing signs of infection themselves, these horses may still be infectious to other horses. For this reason, for maximum protection and to reduce spread, we currently recommend 6-monthly boosters, especially for competition horses. For other horses, including those on private yards that never compete, we advise a minimum of annual flu boosters after completing their primary course.
