Why do we recommend splitting vaccines into two sessions?

 The purpose of vaccination is to stimulate an immune response to a particular antigen (infectious particle, virus or bacteria). When the horse is exposed to the actual virus or bacteria, the body is ready to mount a rapid and vigorous defence, preventing illness and disease.

This “immune system training” can sometimes cause a horse to feel briefly under the weather, have a mild fever, or have soreness at the injection site. Splitting the vaccinations into two separate sessions will reduce the risk of this occurring. In addition, if a horse should be sensitive to a particular vaccine, we will be able to determine which one is the problem if fewer shots are given at one time. 

Another advantage to splitting the vaccines is that we can precisely time certain vaccinations for maximum effectiveness. For example, mosquito-transmitted diseases like West Nile disease peak in late spring and early fall, so it makes sense to place this vaccine in the second round of shots.

Sometimes due to distance or timing, we have to give all of the vaccines at once. Many horses cope with this well, but we have noticed a higher rate of complication under these circumstances. It is a good idea to have some bute or banamine handy in the event of soreness.