1 July 2016
Influenza Protection for the Performance Horse
Brought to you by Merck Animal Health

Performance horses are unique. Their influenza protection should be no different. Because of your horse’s active lifestyle, his risk of contracting influenza is enhanced and his vaccination protocol will differ from horses that are home on pasture. Your veterinarian may recommend the modified-live virus (MLV) intranasal influenza vaccine (Flu Avert® I.N.) for several reasons:

      1. 1) Modified-live virus vaccines activate multiple arms of the immune system – creating a more robust immune response. This is important when dealing with a pathogen such as influenza, which is complex, highly contagious and constantly undergoing change (a phenomenon called antigenic drift).
      2. 2) The MLV, intranasal influenza vaccine is less subject to the consequences of antigenic drift, providing very good protection against the influenza strains infecting horses in the U.S. 1,2,3
      3. 3) The initial site of action is in the upper respiratory tract where the influenza virus gains entry –providing a line of defense where the infectious process starts.
      4. 4) The MLV vaccine requires just one dose and activates immunity quickly – within 10 days – 4 making this ideal for primary immunization or as a booster immunization following any other influenza vaccination. The American Association of Equine Practitioners guidelines also recommend this MLV vaccine during equine influenza outbreaks. 5
      5. 5) The unique intranasal administration leaves no risk for an injection-site reaction that may delay your horse’s return to training or competing.

The most important steps you can take in preventing this highly contagious disease are vaccination and sound biosecurity practices. Work with your veterinarian to determine the most appropriate vaccination protocol for your horse.


1 Chambers TM, Holland RE, et. al. A new modified live equine influenza virus vaccine: phenotypic stability, restricted spread and efficacy against heterologous virus challenge. Equine Vet J. 2001;33(7):630-636.
2 Van de Zande S. Efficacy of Flu Avert IN, a modified live influenza vaccine for horses used in different vaccination schedules against A/Equi-2/South Africa 04/03 Challenge. Efficacy of Flu Avert / Prequenza, a combined vaccination schedule against A/Equi-2/Newmarket/05/03 challenge. Unpublished data.
3 UC Davis (Nicola Pusterla) & Merck Animal Health. Infectious Upper Respiratory Disease Surveillance Program. Ongoing research 2008 – present.
4 Townsend HGG. Onset of protection against live-virus equine influenza challenge following vaccination of naïve horses with a modified-live vaccine. Unpublished data.
5 AAEP Vaccination Guidelines (www.aaep.org)