Vaccination of Horses
Dr. Philip Johnson
Routine vaccination should be part of a comprehensive health maintenance program for all horses. The objectives of vaccination fall into three categories: To prevent disease
To reduce the severity of disease
To minimize the extent to which horses spread the disease
If you have only one horse, then the important aspect is disease prevention; but if you own a big farm, you will reduce the impact of an outbreak.
How Vaccines Work
The horse has an excellent immune system, on par with any other species. However, when nose to nose with a new pathogen (virus or bacteria), the horse's body has no specific defense. In this instance, the horse succumbs to the full range of symptoms. An immune reaction against the infection occurs, and substantial damage may have occurred already.
What you want is a specific immune response, which is one that is directed at the offending pathogen, that recognizes it, and prompts its destruction. Vaccination is intended to prime specific components of the horse's immune system such that, on subsequent exposure to a specific pathogen, the horse is able to mount a much more rapid and effective response to prevent or minimize the clinical symptoms.
Vaccines Currently Available
Most horses in the United States are regularly vaccinated against tetanus, influenza, eastern and western equine encephalomyelitis, rabies and rhinopneumonitis. Vaccines are also currently available to confer protection against viral arteritis, strangles, botulism and Potomac Horse Fever. Under special circumstances, other less commonly used vaccines may be considered. Vaccines should be administered by a veterinarian, as there can be serious mistakes in administration and occasionally allergic reactions. Your veterinarian is prepared to deal with these problems appropriately.
The route of vaccination depends on the product, but vaccines are available for intramuscular, and more recently, intranasal administration.
Most vaccines used in horses are administered by intramuscular injection. There are good reasons for this. First, the skin and subcutaneous tissues of horses are very sensitive to most vaccines and react with a nasty inflammatory reaction if they're given too close to the skin. Second, the blood supply in muscles is excellent, so the vaccine antigens can be picked up by cells that are in close contact with the bloodstream. Vaccines must be given in muscle away from solid structures like ligaments, tendons and bones. A common mistake is to give a vaccine too high in the neck, where it goes into the nuchal ligament rather than muscle.
Vaccines administered in the muscle stimulate the production of antibodies that circulate in the blood and prime the immune system to heighten its level of preparedness for future interactions with specific pathogens.
Whereas most vaccines cause an immune reaction everywhere in the body, some newer vaccines have been developed to stage a defense in a particular part of the body, such as the respiratory system. These vaccines, administered via the intranasal route, may improve immunity against pathogens that target the respiratory system and are intended to provide the lining of the respiratory tract with protective ("neutralizing") antibodies at the entrance site of the pathogen.
Vaccines against both strangles and influenza have been made available for administration to horses via the intranasal route. Although these vaccines have demonstrated some efficacy in field trials, we do not know how long they are effective. To rely on them for protection for over 6 months is too much to expect, so it is important to vaccinate at key times or vaccinate more frequently.
It is recommended that horse owners maintain good records of their horses' vaccinations. Before being allowed to compete at many open horse shows, the rider must often be able to demonstrate (using a vaccine certification passport that has been signed by a veterinarian) that the horse has been vaccinated on a regular basis. This is especially important with respect to the respiratory pathogens.
When purchasing or selling a horse, a well-maintained vaccination record will help demonstrate to prospective purchasers that the horse's health has been carefully protected and there will be no need to start a new vaccination program all over again.