When it comes to routine healthcare for your horse, a flu vaccination given once a year might seem like just another one of those things to remember to have done.

But what could seem like a minor part of your horse's care, taking literally seconds have done, is in actual fact much more important than you may have considered.

Why should we vaccinate?

Studies over the last few years estimate the number of horses in the UK to be around 1m, with additional data suggesting that less than 50% of those horses are vaccinated against equine influenza.

The virus causes a highly contagious respiratory disease which is easily spread from horse to horse, either via the air or by close contact between horses. In 2014, there were at least thirty outbreaks.

The map shown below courtesy of the Animal Health Trust shows the locations of outbreaks. Of course, it is possible this is only the tip of the iceberg as each of these outbreaks represents a horse having a confirmed laboratory diagnosis of flu and not all horses suspected to be infected will necessarily be tested.

Nevertheless, it's clear from the map that equine flu is a problem in all areas of the UK. With this disease being so widespread, keeping your horse's vaccinations up to date seems an obvious way to help protect them.

But we should also consider that, by vaccinating horses against equine flu, we are not just protecting that individual horse: the greater numbers of horses which are vaccinated mean less spread and less risk to the horse population in general, including those which are not vaccinated.

When high percentages of horses are protected by vaccination, the spread of disease is more difficult as there are less susceptible horses available to infect. If we could increase the percentage of horses vaccinated against equine flu to more than 70%, it's likely we would see many fewer outbreaks.

How do vaccinations give protection?

When a vaccination is given, it mimics the horse being infected by the virus itself so that the body can produce antibodies against the virus so that if the horse then is exposed to the virus by coming into contact with an infected horse, the body will be able to more quickly and more strongly respond to the virus.

You could consider that vaccination is priming the body so that it can act more effectively in the face of infection.

Of course, we don't want the giving of a vaccination to cause the disease itself and so vaccines will contain specific parts of the virus in a special delivery system so that they can stimulate the immune system without any signs of illness.

Are all flu vaccinations the same?

In short, the answer is no. There are several different vaccinations on the market in the UK at the moment.

They differ in a number of ways but the main differences are firstly the different strains of flu virus contained in the vaccine and secondly the way the parts of the virus in the vaccine stimulate the body's immune system.

As an owner, the second difference is not particularly important as all vaccines currently in use in the UK have been tested to show that they do adequately lead to antibodies being produced regardless of how they do it.

The first difference, in terms of which strains are contained in the vaccine, are of more interest for the purposes of this article.

In a similar way to influenza in humans, over time the virus evolves and different strains emerge. Until recently, some flu vaccinations still contained strains of virus which had originally been identified in the eighties and nineties.

The World Health Organisation for Animal Health makes recommendations as to which strains are included in vaccines and vaccine companies then have to update which strains are contained in their particular vaccine.

This, however, is not as quick and easy as it may sound as many rounds of testing and safety checks must be made before the vaccine is allowed onto the market.

To make matters more confusing, many of the older vaccines which do not contain the two recommended strains have been shown to protect horses nonetheless.

Within the equine veterinary community the choice of vaccine used is a contentious issue and even the experts cannot agree! In spite of this, it is clear that increasing the numbers of horses vaccinated will help prevent flu outbreaks.