Ask Your Veterinarian Presented By Equistro: Do Equine Vaccines Change Each Year?

by | 01.09.2018 | 11:14am

Q: We've heard a lot about how this year's human flu shot doesn't seem to be as effective as it has been in years past.  Do equine vaccines also get modified from year to year, and if so, how concerned should managers be that a vaccinated horse could get an infectious disease?

A: The short answer is no, equine vaccines don't get modified from year to year like the human vaccine does.

The reasoning for this is multifactorial. First and foremost, antigenic drift (which is the gradual or pinpoint changes in the genotype of viruses that happens continually over time) occurs much faster in humans than in the equine population. Thus, new strains of the influenza virus occur regularly and the human vaccine must be updated in order to attempt to stimulate antibody production that will be protective against the ever-changing virus.  The updated vaccine's efficacy (effectiveness) can be greatly affected, depending on how big of a change in the genotype (antigenic drift) of the virus from year to year.  Because these mutations in the equine influenza virus occur at a much slower rate, the current licensed vaccines for EIV have proven to be more efficacious for longer periods of times (years to decades) when following labeled instructions and boostered appropriately.

Secondly, it is a large financial burden on animal drug companies to go through the process of testing efficacy, safety trials, and gaining licensure when updating their vaccine lines, thus affecting the price of the vaccine to the equine owner.  In equine medicine new or updated vaccines come on the market as the need arises, such as an outbreak or new disease surfaces (example, west nile virus in the early 2000's).  Fortunately, for the equine world there has not been the need to update vaccines yearly to be effective.

Rood and Riddle Equine Hospital's Dr. Dale Brown

The AAEP (American Association of Equine Practitioners) website ( provides vaccination guidelines to veterinarians and horse owners. There are five core vaccines that every horse is recommended to receive that provide protection against those diseases that are deemed “endemic to a region with potential public health significance, required by law, virulent/highly infectious, and/or those posing a risk of severe disease.”  They include: Eastern/Western Encephalomyelitis, Tetanus, Rabies, and West Nile Virus.  Following the core vaccines are risk-based vaccines that are recommended based on region or location of the horse, use of the horse, environmental factors, etc.  Some of these include: Influenza, Rhinopnuemonitis, Botulism, Leptospirosis, Potomac Horse Fever, Strangles, etc.

Proper vaccination in conjunction with good husbandry/managerial practices significantly limit and potentially eliminate infectious disease outbreaks at the individual or herd level.  It is recommended to isolate all new horses for a minimum of 14 days before introducing them to others.  As always, it's recommended to consult with your veterinarian on an appropriate set of vaccination/herd health guidelines specific to your horse or farm.

Dr. Dale Brown was raised on a cow/ calf farm in Girard, Kansas. After working on a Quarter Horse breeding farm during high school, he decided to attend Kansas State to pursue an Animal Science/ Agribusiness undergraduate degree. He earned his degree in 2001 and continued his schooling at Kansas State obtaining his Veterinary Medicine degree in 2006. Dr. Brown completed his Ambulatory Internship with Rood & Riddle in 2007. He joined Rood & Riddle as an associate in 2007 and in 2013 he became a shareholder. Dr. Brown's special areas of interest include reproduction, neonatal medicine, herd health, and public yearling sales. When not seeing patients, Dr. Brown enjoys spending time with his wife Kelly, his daughter Samantha and his twin boys, Wyatt and Clayton. He also is an avid college sports enthusiast.

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