So why do we vaccinate horses against equine influenza? Clinical signs vary from a mild cough to severe acute respiratory disease but it is unlikely to be fatal. It is however, extremely contagious and can therefore spread rapidly through the equine population. In 2007 an outbreak in Australia, a country in which the vast majority of horses were not vaccinated, resulted in widespread disruption to the equine industry at a cost of around A$1 billion! In the UK, the exact percentage of vaccinated horses is not known, but based on vaccine sales versus the estimated equine population, only 30-40% of horses are covered which is surprisingly low. Equine Influenza is an endemic disease in this country so there are always infected horses about. It is up to us as Veterinary Surgeons to identify potential cases, isolate them and submit samples for testing so that we keep track on this virus. This testing is free due to funding by the Horserace Betting Levy Board and involves taking nasopharyngeal swabs looking for viral DNA by qPCR and paired serum samples looking for an increase in antibody levels. The optimum time to detect via qPCR is between 2 and 5 days following exposure. We are very fortunate in the UK to have the Equine Infectious Disease Surveillance Team (EIDS) funded by the Thoroughbred industry, based at Cambridge University to monitor equine infectious diseases and to advise in the event of an outbreak. The last significant epidemic to occur in the UK was during 2019, when there were 412 confirmed cases on 234 premises. 72% of these cases were unvaccinated. New horses had arrived at the yard within two weeks of a confirmed case in 42% of outbreaks, reaffirming the sense in quarantining/isolating and monitoring clinical signs. Going back to the original question of why we vaccinate; a vaccinated horse will have greater protection in the event of exposure to virus and he or she ,will shed less virus especially if they have had a recent booster. If we want to compete our horses we need to abide strictly to the vaccination requirements of the various governing bodies overseeing competitions. There are some variations between different bodies and we will try and summarise these below: The British Horseracing Authority (BHA) were instrumental in introducing changes to the equine influenza vaccination protocols following the 2019 outbreak.
New equine influenza vaccination rules came into effect on 1 January 2023, following a 12-month transition period to help trainers adjust to the changes.
These require all racehorses to be vaccinated in line with the new primary course and booster vaccination interval schedules set out below:
As you will see from the table below, some organisations have followed the BHA initiative with respect to primary vaccination courses. It would make everyone’s lives easier if there was one protocol across all disciplines :
