Are Horses Vaccinated Against Influenza Still Susceptible?

A horse down the road was just diagnosed with equine influenza virus (EIV). But you don't have to worry because your horse is vaccinated against the virus, right? Wrong. Equine infectious disease experts have recently determined that influenza vaccination breakdowns are common, making even vaccinated horses susceptible to the disease.

 

“Overall, equine vaccines commercially available in the United States are both safe and efficacious; however, suboptimal protection of vaccines can and do occur,” said Nicola Pusterla, DVM, PhD, Dipl. ACVIM, professor of equine internal medicine, chief of large animal medicine, and section head of equine medicine and dentistry at the University of California, Davis, School of Veterinary Medicine.

 

Vaccine breakdowns are particularly common with viruses (rather than bacteria) that are capable of mutating, because the body essentially sees them as a new disease-causing organism. As a result, the horse’s immune system is not “primed” against the new version of the virus, making them susceptible to infection (which can produce clinical signs including high fever lethargy, nasal discharge, and coughing).

 

Pusterla and colleagues discovered these widespread occurrences of vaccine breakdown in horses vaccinated against EIV after collecting data on 2,605 horses with signs of respiratory disease from 38 states over a 45-month period. Of those, 239 tested positive for EIV, 84 of which had been vaccinated against EIV (the time of vaccine administration ranged from less than 6 months to more than a year prior).

 

“The number of EIV-positive horses that had been vaccinated against EIV in our current survey was statistically higher than previously reported in 2008, suggesting that the occurrence of vaccine breakdown is increasing,” said Pusterla.

 

Video: Evolution of Beef Cattle Farming

The Clear Conversations podcast took to the road for a special episode recorded in Nashville during CattleCon, bringing listeners straight into the heart of the cattle industry. Host Tracy Sellers welcomed rancher Steve Wooten of Beatty Canyon Ranch in Colorado for a wide-ranging discussion that blended family history and sustainability, particularly as it relates to the future of beef production.

Sustainability emerged as a central theme of the conversation, a word that Wooten acknowledges can mean very different things depending on who you ask. For him, sustainability starts with the soil. Healthy soil produces healthy grass, which supports efficient cattle capable of producing year after year with minimal external inputs. It’s an approach that equally considers vegetation, animal efficiency, and long-term profitability.

That philosophy aligned naturally with Wooten’s involvement in the U.S. Roundtable for Sustainable Beef, where he served as a representative for the Colorado Cattlemen’s Association. The roundtable brings together the entire beef supply chain—from producers to retailers—along with universities, NGOs, and allied industries. Its goal is not regulation, Wooten emphasized, but collaboration, shared learning, and continuous improvement.