‘Flu’ is a viral respiratory disease that affects horses of all ages although younger horses more commonly show clinical signs of illness (raised temperature, discharge from the eyes and nostrils and coughing). Whether obvious signs are shown or not, equine influenza infection can result in days or weeks off work and the virus rapidly spreads to other horses by nasal aerosol (coughing). Life threatening sequelae also develop rarely in some horses such as myocarditis.
Specific vaccinations reduce both the chance of becoming infected, if challenged, and the severity of illness, if infection occurs, allowing more rapid recovery, as well as reducing the risk of spread to other horses. Different types of equine influenza vaccine are available and manufacturers have different recommendations for their vaccination programme. Most vaccines also combine equine influenza with tetanus.
- The first two (primary) vaccinations are given 21 to 92 days apart (generally four weeks).
- The third vaccination is given 150 to 215 days after the primary vaccination course. To conform to British Horseracing Authority (BHA) or Fédération Equestre Internationale (FEI) rules, this third vaccine must be given five to seven months after the second primary vaccination.
- Racehorses must not have been vaccinated on the day of a race or on any of the six days prior to the day of the race in which a horse is declared to run. Horses competing under FEI rules must have been vaccinated within six months but not within seven days before arrival at the event.
- Subsequently, booster vaccinations are given at least at 12 monthly intervals but there is some clinical evidence that booster vaccinations given at six months intervals do provide better protection especially in younger horses. BHA and some manufacturers recommend 12 month intervals but experience of vaccine ‘breakdown’ in the face of field infection, suggests this is insufficient to give adequate protection.
- Foals can be vaccinated against influenza from six months of age.