Protecting Horses Against the Growing Flu Threat

Research shows equine influenza vaccines and vaccination practices must evolve to keep up with changing flu strains.

There’s much ado about flu of late and with good reason. The incidence of equine influenza virus (EIV) has trended upward since 2008. It was the most common infectious upper respiratory disease of the horse in 2019.¹,² Of the horses with known vaccination status, 61% of positive EIV cases occurred in horses vaccinated against EIV.²

What’s driving this apparent EIV vaccine failure? Antigenic drift, according to researchers at the University of California, Davis School of Veterinary Medicine. Their findings show that rather than foreign EIV strains being introduced into the U.S., native flu strains are changing.³

Case in point: The 2013 influenza outbreak that occurred in Florida in a large number of well-vaccinated horses. Researchers with Merck Animal Health’s found those horses were infected with a new flu strain, named Florida ’13 after the location and date of first isolation.

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