With some vaccines, a series of doses may be required for the immune response to reach effective levels. The presence of the vaccine programs immune cells to be aggressive towards specific disease-causing organisms. This immune cell programming weakens at a steady rate after the immune response has reached its peak. When immunity falls below protective levels, a booster vaccination is an effective way to stimulate immunity. Stenbom says timing is an essential ingredient to consider when vaccinating.
Individual vaccines vary in the duration of immunity they provide.
While some vaccines provide only enough immunity for two to four months, others provide protection for an entire year. A horse that faces a severe disease challenge shortly after vaccine administration, or one that is already incubating the disease cannot expect to be protected from the illness. Horses that are exposed to other horses, unfamiliar environments and are traveling face more severe disease challenges. Ideally, the best time to vaccinate is when your horse is free of disease, under relatively little stress, and in good condition. This increases the probability of an effective long-lasting immune response.