Every horse in North America needs five core vaccines: tetanus, rabies, Eastern equine encephalomyelitis (EEE), Western equine encephalomyelitis (WEE), and West Nile virus (WNV). These are considered essential for all horses regardless of age, breed, or lifestyle because the diseases they prevent carry a high risk of death. Beyond these five, several additional vaccines are recommended depending on where your horse lives, how often it travels, and whether it’s a broodmare or young foal.
The Five Core Vaccines
The American Association of Equine Practitioners (AAEP) classifies these vaccines as core because the diseases are widespread, often fatal, and in the case of rabies, a direct threat to human health. All five require annual boosters for previously vaccinated adult horses.
Tetanus
Horses are extremely susceptible to tetanus, which is caused by bacteria commonly found in soil. Any wound, even a small puncture, can introduce the bacteria. The tetanus toxoid vaccine is one of the most effective equine vaccines available, producing strong protective antibodies with routine annual boosters. If your horse sustains a wound or has surgery more than six months after its last tetanus booster, it should get an additional dose at the time of injury.
Rabies
Rabies is always fatal once symptoms appear, and an infected horse can transmit the virus to people. A single dose is given annually. Unlike some vaccines that require a multi-dose primary series in adult horses, an unvaccinated adult only needs one initial dose followed by annual revaccination.
Eastern and Western Equine Encephalomyelitis
EEE and WEE are mosquito-transmitted viruses that attack the brain. EEE is particularly deadly, killing up to 90% of infected horses. These two vaccines are typically combined in a single product. Annual revaccination should be completed in the spring before mosquito season begins. In areas experiencing an early or heavy disease season, your veterinarian may recommend more frequent dosing to maintain protective immunity during peak exposure.
West Nile Virus
Also spread by mosquitoes, West Nile virus causes neurological disease that can range from mild coordination problems to complete paralysis. The vaccine is given annually in the spring, timed so immunity peaks during insect season. Horses in southern states with year-round mosquito activity may benefit from boosters every six months.
Risk-Based Vaccines
Beyond the core five, several vaccines fall into a “risk-based” category. Whether your horse needs them depends on factors like geography, travel frequency, exposure to other horses, and reproductive status. Common risk-based vaccines include:
- Equine influenza: Recommended for horses that travel, compete, or are frequently exposed to new horses. Previously vaccinated adults get an annual booster, but horses at higher risk of exposure may need revaccination every six months. Many competitions and boarding facilities require proof of an influenza vaccine within the past six months.
- Equine herpesvirus (EHV-1 and EHV-4): These viruses cause respiratory disease, and EHV-1 can also cause neurological disease and abortion in pregnant mares. Horses that mingle with large groups or travel to shows are the primary candidates.
- Strangles: A highly contagious bacterial infection of the upper respiratory tract. Two vaccine types exist. The intranasal modified-live vaccine stimulates a high level of immunity but can cause temporary nasal discharge or mild swelling in some horses, especially those under two years old. The injectable killed vaccine is associated with more injection-site reactions and has a lower reported efficacy, reducing clinical disease by roughly 50%. Your vet will help choose the right option based on your horse’s history and risk.
- Potomac horse fever: A concern in areas near rivers and streams where the disease-carrying parasites thrive.
- Botulism: Particularly relevant in the mid-Atlantic region and for horses fed round bales or haylage, which can harbor the toxin-producing bacteria.
Foal Vaccination Schedules
Foals don’t follow the same simple annual schedule as adult horses. Their immune systems are immature, and maternal antibodies passed through the mare’s colostrum can interfere with early vaccination. The timing of a foal’s first vaccines depends heavily on whether the mare was vaccinated.
For foals born to vaccinated mares, the primary series for most core vaccines starts at 4 to 6 months of age. This gives time for maternal antibodies to decline enough that the vaccine can stimulate the foal’s own immune response. A typical schedule looks like a first dose at 4 to 6 months, a second dose 4 to 6 weeks later, and a third dose at 10 to 12 months. Rabies is slightly different: the first dose is given at 6 months, with a second dose 4 to 6 weeks after.
Foals born to unvaccinated mares lack that borrowed maternal protection and need to start earlier. For tetanus, the first dose can be given as young as 1 to 4 months, with two follow-up doses spaced about 4 weeks apart. For EEE/WEE, West Nile, and rabies, the series typically begins at 3 to 4 months. These foals are more vulnerable in their first weeks of life, so managing their environment and limiting exposure to other horses matters until the vaccine series is complete.
Broodmare Vaccination Timing
Pregnant mares have a unique vaccination schedule designed to accomplish two things: protect the mare herself and load her colostrum with antibodies that will shield her foal during its first months of life.
Core vaccines (tetanus, EEE/WEE, WNV, and rabies) are typically boostered 4 to 6 weeks before the expected foaling date. This timing ensures peak antibody levels in the colostrum when the foal nurses for the first time.
Equine herpesvirus deserves special attention in broodmares. EHV-1 can cause late-term abortion, and the standard prevention protocol is a three-dose series given at months 5, 7, and 9 of gestation using a product specifically labeled for abortion prevention. A separate respiratory-targeted booster is also recommended 4 to 6 weeks before foaling.
Timing and Seasonal Considerations
For most adult horses in temperate climates, the annual vaccine appointment happens in late winter or early spring. This ensures immunity is strongest heading into mosquito season, when the risk of EEE, WEE, and West Nile virus climbs. Horses in the deep South, Florida, or Gulf Coast regions where mosquitoes are active nearly year-round may need a second round of mosquito-borne disease vaccines in the fall.
Horses that show, race, or board at facilities with frequent turnover face a higher ongoing risk of respiratory infections. For these horses, influenza and herpesvirus vaccines on a six-month cycle, rather than annually, provide better continuous protection. If your horse rarely leaves the property and doesn’t encounter new horses, an annual schedule for risk-based vaccines is usually sufficient.
What a Typical Annual Schedule Looks Like
For an adult horse that has been previously vaccinated, a straightforward annual plan covers the following:
- Spring (before mosquito season): EEE/WEE, West Nile virus, tetanus, rabies. These are often available as combination products, so your horse may only need one or two injections to cover all five core vaccines.
- Spring or as needed: Influenza, EHV, strangles, and any other risk-based vaccines appropriate for your horse’s lifestyle.
- Fall (if applicable): Booster for mosquito-borne diseases in high-risk regions, or influenza/EHV boosters for horses that travel heavily.
Unvaccinated adult horses or those with an unknown history need a primary series, which usually means two doses spaced 4 to 6 weeks apart, followed by annual revaccination. Rabies is the exception, requiring only a single initial dose before moving to annual boosters.