Several equine infectious disease outbreaks already have occurred in 2016. Quarantine measures and other steps to help prevent the spread of disease associated with these outbreaks have grabbed the headlines for good reason. Yet, many horse owners are left scratching their heads wondering what role vaccination has or could play in preventing these situations. What went wrong, if anything?

An ongoing equine respiratory disease surveillance program could shed some light on this subject. The surveillance program, being conducted by Merck Animal Health in partnership with University of California, Davis, School of Veterinary Medicine, is uncovering information that underscores the importance of basic biosecurity in preventing the spread of infectious disease. Some of these findings were presented at the International Equine Infectious Disease Forum, which took place in April in Buenos Aires, Argentina.

“Vaccination with inactivated influenza vaccines alone may reduce clinical signs of disease and shorten the recovery period, but may not provide complete protection, as hoped or often expected,” said Wendy Vaala, VMD, Dipl. ACVIM, Merck Animal Health associate director of life-cycle management, who presented the findings.

As an example, 36% of equine influenza cases since the surveillance program began in 2008 occurred in vaccinated horses. The study also has debunked the long-held belief that many infectious upper respiratory diseases, such as influenza, are more common in young horses. Demographic data collected from positive cases associated with recent influenza outbreaks shows an age range from 8 months to 22 years, and a diverse horse population representing a variety of disciplines and travel patterns