Equine Influenza Virus
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Equine Influenza Virus

Equine influenza, also known as 'flu', is an infectious disease which affects the upper respiratory tract of horses. There have been frequent outbreaks in the UK in recent years.

Clinical signs usually appear within 1–5 days of exposure to the flu virus and they can last for 3–6 weeks. Signs can include a high temperature, cough, nasal discharge, enlarged glands (under the lower jaw), conjunctivitis, depression, loss of appetite and filling of the lower limbs.

BEVA equine influenza position statement

We recommend that all horses are vaccinated against equine influenza.

An initial primary course of two vaccinations must be given: the second vaccination must be administered within 21-60 days of the first vaccination.

The first booster must be administered within 6 calendar months following the date of the administration of the second vaccination of the primary course.

Note: individual horse owners are advised to follow their vets’ advice on the intervals recommended by the manufacturer for the specific product used (typically 4 or 4-6 weeks between the 1st and 2nd vaccine and 5 months between the 2nd and 3rd vaccine).

A minimally appropriate subsequent booster schedule can be considered. Booster vaccinations must be administered at a maximum of 12 months intervals. We strongly endorse an optimal schedule achieved by increasing the frequency of boosters to within 6 months.

    In deciding whether to follow the “minimally appropriate” or “optimal” vaccine schedules outlined above, we urge horse owners and their vets to consider the following points:

    • The primary aim of flu vaccination policies is to protect individual horses from clinical illness should they encounter equine influenza virus.
    • There is considerable scientific evidence to support the assertion that horses which are vaccinated at six monthly intervals are protected more effectively from clinical signs of flu than those vaccinated at 12 monthly intervals and are less likely to transmit infection.
    • Additional benefit can be gained by administering boosters strategically, i.e. at the times of year corresponding with periods of increased horse gathering and consequent increased risk.
    • Influenza virus spreads via the airborne route and has the ability to spread rapidly over distances in excess of those found on a typical equestrian premises, whether indoor or outdoor. Farm-to-farm airborne spread is possible in many regions of UK.
    • The response to vaccination is not immediate and there must be an interval of at least 7 days between the most recent vaccine dose and mixing with other horses to have some benefit from that recent vaccine. This is a particularly important point to consider when introducing a recently vaccinated new animal to a property.
    BEVA endorses 6 month flu boosters

    Science advances, "label claims" rarely do. We have the freedom to recommend the use of products “off label” or to use unregistered products where it is appropriate to do so in accordance with the veterinary cascade. This also extends to our use of vaccinations in practice. Our responsibility is to act in the best interests of the horses under our care and the evidence is unequivocal that in higher risk populations better protection is afforded by vaccination at 6 monthly intervals rather than 12.

    6 month vaccine infographic

    Download our useful infographic to easily communicate the benefits of 6 monthly influenza vaccinations.


    EVJ in Conversation: bi-annual boosters

    In this podcast, Richard Newton discusses equine influenza bi-annual boosters following his editorial in Equine Veterinary Journal.


    Published research and editorials
    1. Equine influenza vaccination catches an autumn cold! But must get over it as soon as it can
    2. J. Richard Newton, David I. Rendle, David R. Mountford, Celia M. Marr First published 13 October 2022, Equine Veterinary Journal

    3. Equine influenza bi-annual boosters: What does the evidence tell us?
    4. Victoria A. Colgate, J. Richard Newton First published 16 November 2022, Equine Veterinary Journal