HOW IT WORKS: In common with most vaccines, the active part of EHV vaccines is created from part of the virus that has been chemically modified to create an immune response without creating disease. When this product is injected into the muscle, the viral part is recognized by immune cells, which create antibodies to that part over weeks. If the virus later gains access to the blood or respiratory tract, the antibodies bind to that part of the virus and destroy it before it can produce signs of disease.

EHV-4/1 vaccines are somewhat helpful against the respiratory disease, which usually presents as nasal discharge and cough. Unfortunately, vaccination does not prevent the neurologic form of disease. It may, however, reduce the spread of EHV-1 generally, thus reducing overall disease incidence in a group of horses.

These risk-based vaccines should be given twice annually, by either intramuscular or intranasal routes, depending upon the specific product.

Pregnant mares should be vaccinated as directed with a vaccine licensed to protect against the abortive form of the disease. Generally this is at months 5, 7 and 9 of pregnancy. These are different products than those intended to prevent respiratory disease.

Talk to your vet to determine whether your horse needs these vaccines. Horses in contact with others (show and performance horses, horses boarded at barns) are at greater risk for EHV and so might benefit from vaccination. There is probably less benefit for older and isolated horses.

If you decide to vaccinate for EHV, be sure to use the right product. Involve your vet in your vaccination program: They know about the more effective vaccines, can ensure that the vaccine is handled and administered properly, and will address any complications if they arise. If your vet administers the vaccine and your horse contracts the virus, some pharmaceutical companies will pay for at least a portion of the veterinary treatment required.