Staying up-to-date with required vaccines is important to keep your horse healthy and prevent the spread of infectious diseases.

Vaccines have been developed for 14 major equine diseases, including Strangles, West Nile Virus, Equine Influenza, and Equine Herpesvirus.

Some vaccines are recommended for all horses, while others are recommended based on your horse’s risk profile. If your horse lives in specific geographic areas, competes in performance disciplines, or frequently travels to events and shows, they may have a higher risk of contracting certain diseases.

Consult with your veterinarian to determine which vaccinations are recommended for your horse and to plan your annual vaccine schedule. As the saying goes, “An ounce of prevention is worth a pound of cure.”

Equine Vaccines

Vaccines are biological substances that stimulate the horse’s immune system to protect against diseases.

Vaccines can be made of either dead or weakened forms of viruses, bacteria, pathogenic organisms or other substances that cause disease in horses.

When administered to a horse, they trigger the body’s immune response to produce antibodies so the horse can recognize and fight the virus or bacteria if it is encountered in the future.

Antibodies are special proteins that attach themselves to foreign invaders in order to neutralize them. These antibodies remain in the horse’s system for weeks or months after vaccination, providing immunity against targeted diseases.

How Do Vaccines Work?

The immune system can be divided into two parts: the innate immune response and the adaptive response.

The innate immune system is the body’s immediate protective response to infection that attempts to kill the pathogen and prevent it from spreading.

The adaptive immune response is not active immediately when the horse is infected but rather develops in response to the specific pathogen affecting the horse.

Consequently, if the horse is reinfected with the same pathogen, the adaptive immune system mounts a stronger, faster response providing better protection or immunity against the pathogen.

Adaptive Immune System

The adaptive immune system responds in two ways: the cell-mediated response and the humoral response.

The cell-mediated response is carried out by T-lymphocytes (T-cells). T-cells work together with the innate immune system to recognize antigens, amplify the body’s immune response and destroy the pathogen.

The humoral response involves white blood cells known as B-cells (lymphocytes) and immunoglobulins (antibodies).

These immune cells detect structures on pathogens called antigens and respond by neutralizing the invading pathogen, so it is no longer harmful. B-cells also store a memory of the antigen so the horse’s body can fight back more efficiently against future infections.

Newborn foals develop immunity against diseases through the passive transfer of antibodies from their mother. When a mare has immunity to a specific disease, immunoglobulins (antibodies) are passed to her foal in colostrum, providing protection to the foal against the same disease.

How to Administer Vaccines

Vaccines must be administered by or under the supervision of a veterinarian. [3]

The location of injection is chosen to minimize adverse reactions to the vaccine and to maximize the safety of the horse and the person administering the vaccine. [3]

The ideal injection site is a large muscle that is used by the horse a lot, such as the base of the neck or the hamstring. [3]

Neck injections should be administered at the base in an area surrounded by the crest of the neck (nuchal ligament), the shoulder blade, and the cervical vertebrae, which run from the poll to the shoulder. The hamstring muscle can be injected at least one inch below the tuber ischii bone in the horse’s rear.  [3]

Types of Vaccines

Vaccines initiate the body’s adaptive immune response, so the horse develops immunity against a pathogen without developing a clinical infection.

Several types of vaccines have been developed using different methods of stimulating an adaptive immune response. Types of vaccines include inactivated, modified live, recombinant, toxoid, subunit and DNA vaccines.

Inactivated Vaccine

Inactivated or killed vaccines are made by treating the targeted pathogen with heat or chemicals to inactivate or kill it. The pathogen can then be administered in the vaccine without harming the horse. [2]

Inactivated vaccines are made using an adjuvant which helps the vaccine elicit an immune response in the horse. [2] These vaccines are easy to store and are usually very safe because the pathogen is no longer effective. [2]

Immunity from inactivated vaccines develops slowly and often requires multiple doses and boosters. This type of vaccine causes a humoral response but is less effective at eliciting a cell-mediated immune response in the horse. [2]

Modified Live (Attenuated) Vaccine

Modified live vaccines (MLVs) are also called live attenuated vaccines because they are made with an attenuated or weakened pathogen. MLVs are made by mutating parts of the pathogen to elicit an immune response in the horse without causing harmful clinical signs. [2]

MLVs cause a stronger and longer-lasting cell-mediated and humoral immune response than inactivated vaccines. MLVs also require fewer doses and do not require an adjuvant. [2]

MLVs must be stored carefully according to the manufacturer’s instructions. MLVs also pose slight