Equine influenza or flu is a common contagious disease in horses. Clinical signs include fever, nasal discharge, and a persistent dry hacking cough that may last for several weeks. Horses usually recover from the disease in several weeks unless a bacterial infection develops as a consequence of the original problem.

You may be think that your horse is not susceptible because he's been vaccinated for the flu, and hopefully you are correct. However, Dr. Steve Grubbs from Boehringer indicates in the Remuda magazine that all influenza vaccines are not created equal because the influenza virus undergoes a process called antigenic drift. In antigenic drift, the proteins on the surface of the virus change, and even a small change makes the vaccine less effective or sometimes ineffective. For this reason, human flu vaccines are reformulated yearly to keep up to date with the most current strains, and it is just as important for equine vaccine companies to keep up too. An equine surveillance panel made up of experts monitors current strains of equine influenza worldwide, and makes recommendations for viral strains that should be included in the vaccines. So not all flu vaccines for horses may be up to date as different vaccines have different strains, and the most effective ones are the ones that are regularly updated. To determine the best vaccine for your horse, consult with your veterinarian to make sure you are doing the best you can to protect him. Choosing your vaccine from testimonials on a website or by price is not a good plan as it is more likely these options will lead to vaccine failure and will be more expensive in the long run.