Many owners feel an injection is all that's needed to safeguard their horses, but there is a difference between immunization and vaccination. It's important to choose the optimum time for vaccination in order to stimulate immunity in the horse. So when a disease-causing organism comes along, the horse's immune system will be able to reject it. To achieve that requires more work than just jabbing the horse with a needle. Timing is one of those things. If insects transmit the disease and you live in Wisconsin there is little reason for you to vaccinate for eastern/western equine encephalomyelitis in the winter. On the other hand if you live in Florida you may need to consider vaccinating more than once a year because of the year-round insect population. Also, vaccinating the horse before travel or an event in enough time is important for adequate protection.
The AAEP stresses that there are certain vaccinations that every horse should receive regardless of where it lives. This is because of either the uncontrolled risk of the disease or the concern that the outcome of infection would be harmful. Rabies is now considered core for large animals. Not many horses get infected so the risk of exposure may be fairly low. But once contracted rabies is fatal, and there is significant public health concern. There was an incident in Tennessee at the Walking Horse Celebration in 2006 where a horse was identified as being rabid. Possibly up to 150,000 people could have been exposed during the show. If the horse had been vaccinated it would have been a different story. So now rabies is included in the core vaccines. Core vaccines include: rabies, tetanus, eastern/western equine encephalomyelitis, West Nile virus. Your veterinarian will help you determine when and how many times these vaccination are needed for your horse.
Risk-based vaccinations vary regionally and within populations. A veterinarian will help you evaluate whether vaccines in this group are right for your situation. You can't vaccinate for everything just to be on the safe side and expect the immune system to respond. A better strategy is to evaluate an individual's risk and vaccinate appropriately. Risk-based vaccinations include: strangles, anthrax, botulism, equine herpesvirus (rhinopneumonitis), equine viral arteritis, equine influenza, Potomac horse fever, rotaviral diarrhea.
For a complete list of vaccination guidelines visit www.aaep.org/vaccination_guidelines.htm