First broadcast on on August 28th 2000.

This information is provided by Provet for educational purposes only.

You should seek the advice of your veterinarian if your pet is ill as only he or she can correctly advise on the diagnosis and recommend the treatment that is most appropriate for your pet.

Flu is a serious disease in horses mainly because it is so highly infectious and because of the devastating effect that it can have on a horses performance

Signs of flu in horses are a cough and a mild fever, but in working horses their athletic performance can be severely affected, so preventative vaccination against the disease is very important, and it is mandatory for many competing horses and ponies such as those competing under Jockey Club Rules.

Like flu in humans and other species one form of the virus that causes flu (in the case of horses it is mainly Orthomyxoviridae Type A virus) has many strains and the different vaccines that are available contain different strains of the virus. 

In the UK the following virus strains are contained in the vaccines listed below *

Vaccine Name Manufacturer Virus Strains in the Vaccine
Duvaxyn IE Plus Fort Dodge Inactivates antigens of equine influenza virus A, strains : 
  • equi1/Prague 56
  • equi2/Miami 63
  • equi2/Suffolk 89
Equip F Schering-Plough Inactivated antigens of equine influenza virus A, strains :
  • equi1/Newmarket 77
  • equi2/Brentwood 79
  • equi2/Borlange 91
Prevac PRO Intervet Inactivated antigens of equine influenza virus A, strains :
  • equi1/Prague 56
  • equi2/Newmarket 1/93 (American type strain)
  • equi2/Newmarket 2/93 (European type strain)

* Source Compendium of Data Sheets for Veterinary Products  2000-2001 Published by NOAH. 

All the viruses in these vaccines are inactivated - which means they should not cause serious signs of flu as a side-effect. These vaccines are also available combined with tetanus vaccine giving protection against the two diseases in one vaccination.

Equine Flu vaccines should be given as follows :

  • Only to healthy horses and ponies
  • To horses and ponies over a certain age (4-5 months) specified by the manufacturers in their data sheets
  • By intramuscular injection
  • The initial course consists of 2 vaccinations 4-6 weeks apart.
  • Repeat vaccines are given 5-7 months and again 12-18 months after the initial course.
  • Thereafter a booster vaccine is advised every 12 months, although horses exposed to the virus may be vaccinated at 6 monthly intervals.
  • Pregnant mares can be vaccinated and it is usually recommended that they be vaccinated 4-8 weeks before the foal is due to be born.

Side-effects and reactions to the vaccine do occur from time to time including :

  • Local swelling at the injection site
  • Abscess formation at the injection site
  • Allergic reactions (rare) - these require emergency treatment by your veterinarian

Unfortunately other viruses can also cause equine influenza, and of course these vaccines do not provide protection - so a vaccinated horse or pony can still develop flu due to other viruses even if it is fully vaccinated.

Like most vaccines there are certain circumstances under which the vaccine may fail to produce an adequate amount of immunity in an individual horse or pony, including the following :

  • If the vaccine has been stored incorrectly
  • If the vaccine has been administered incorrectly
  • The animal has a natural (genetic) resistance to the vaccine
  • The animal (especially young foals) have immunity against the vaccine which they have inherited from the mother
  • The animal has a poor immune system at the time of the vaccination and can't respond properly
  • The animal is too young to mount a good immune response to the vaccine
  • The animal has an infection
  • The animal has poor nutritional status
  • The animal is on drug therapy
  • The animal is under stress

Local circumstances vary, and your veterinarian will advise you about the most appropriate vaccine for your horse or pony, and when best to give the vaccine and boosters.


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