Accelerated Vaccination Combats Horse Influenza Outbreaks

Equine influenza (the "flu") used to be considered a mere annoyance by many, but major outbreaks such as H1N1/swine flu in humans and the Australian equine influenza outbreak of 2007 have changed our thinking. These days, when a flu outbreak is reported, masks, hand sanitizers, and shots run out faster than bread and milk before a winter storm.

Vaccinating unprotected members of an at-risk horse population during an influenza outbreak has not always been recommended for various reasons, a primary one being that a protective immune response to typical killed-virus vaccines was not rapid enough with the recommended 4-6-week interval between the two initial shots required. However, one study has found that accelerating the vaccination schedule to only a two-week interval with a particular vaccine type might help control an equine influenza outbreak.

Charles El-Hage, BVSc, lecturer in veterinary clinical medicine and surgery at the University of Melbourne, Australia, discussed the study at the 2009 American Association of Equine Practitioners convention, held Dec. 5-9 in Las Vegas, Nev. Researchers vaccinated 14 naive Thoroughbreds (horses that had never been vaccinated against, or exposed to, influenza) with two doses of a recombinant canarypox-vectored equine influenza vaccine (ProteqFlu-Te, France) given 14 days apart, and he measured antibody levels before vaccination and out to 224 days after the first shot.

They found antibody levels following this schedule were similar to those found to be protective in horses given the same vaccine on the recommended 4-6-week interval between doses. This is markedly different than results of similar studies using inactivated (killed-virus) vaccines, reported El-Hage. Another benefit of this particular vaccine is that it allows investigators to differentiate the immune response to vaccination from that due to disease.

With an outbreak like the Australian one, where there was a massive susceptible population (Australia was previously free of influenza and vaccination was illegal), El-Hage noted, "This strategy could be used to create 'buffer zones' as a sort of 'immunological back burning' around infected zones, like burning the areas around a wildfire to reduce the amount of available fuel for the fire to spread."

"This accelerated vaccination schedule conferred rapid and long-lasting immunity to EI, and it will enable vaccination to be used strategically to ameliorate the impact of an EI outbreak on susceptible horses," researchers concluded.

About the Author

Christy M. West

Christy West has a BS in Equine Science from the University of Kentucky, and an MS in Agricultural Journalism from the University of Wisconsin-Madison.

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