? Equine influenza, is vaccination really necessary?

Flu vaccination” is the bane of many horse openers’ lives. Making sure your horses are up to date for travelling or competition, or even staying away, can be a nightmare! So is it really necessary?Or is it just a box-ticking exercise? Vet Avice O’Connor investigates the medical need for the influenza vaccine in horses.

What is equine influenza, and is it serious?

Equine influenza is a highly infectious respiratory disease of horses. Affected animals typically show clinical signs within as little as one day of exposure to the virus, although it can be up to five days after exposure. The most commonly seen symptoms are high temperature, cough, nasal discharge, lethargy and loss of appetite. An increase in temperature (above 38.5C) is often the first symptom. Signs of illness can last for 3-6 weeks. Many horses will need a prolonged period of recovery before they can resume athletic work. It is recommended as a general rule that most horses should be rested for one week for each day of illness to minimise the risk of damage to the heart or lungs. 

Once a horse is infected, they are very contagious

Influenza can spread through a yard or competition venue with speed. In populations that are unvaccinated and with no history of infection, up to 100% of horses can be affected. Like many other respiratory infections, the virus is spread by coughing and by environmental contamination. It is very easy for the virus to be transmitted on contaminated clothing or surfaces. This means that any people working with, or around infected horses can easily facilitate viral spread. 

Some affected animals can suffer secondary complications such as pneumonia or lower limb swelling. These are more concerning in older or very young horses, or in those with a previous history of respiratory disease and can be fatal, although fortunately this is rare. 

Vaccination

Without doubt, vaccination is the most effective way of reducing the risk of the disease. However, the percentage of horses vaccinated in the UK may be as low as 30%. (Based on vaccine sales and the horse population). The majority of horses vaccinated tend to be those in work or competing, with retired or companion animals less likely to be vaccinated regularly. 

However, there are some key points to consider:

Vaccination does not guarantee complete immunity

Just like in humans, the flu virus can mutate over time, and as such some vaccines may

 confer greater levels of immunity than others depending on the circulating strain. A variety of vaccines are commercially available, with slightly different strains. Even if the vaccine