Equine Vaccinations for Year-Round Protection
Vaccination isn’t a once-a-year checkbox. It’s a year-round strategy built around your horse’s risk
by A.E. Robinson
Sponsored by:
Photo: Courtesy Boehringer Ingelheim
“ ‘You mean to tell me my $200,000 horse just died because they didn’t get a $50 vaccine?’
“It was one of the saddest things I have ever heard, and as a vet I never want to hear that again. What a terrible waste of life,” says Dr. Sally DeNotta, associate professor and clinician at the University of Florida College of Veterinary Medicine, in Gainesville.
Just three weeks earlier a client had imported the horse from Europe to Florida, a state where Eastern equine encephalitis (EEE) virus circulates in mosquito populations. The horse, assumed to have been vaccinated before importation, developed a fever and neurologic signs and had to be euthanized.
The horse, receiving exceptional care, had just died from a mosquito-borne disease—in February, when much of the Northern Hemisphere isn’t thinking about mosquito control.
Photo: FEI/Jon Stroud Media
“It’s a common misconception among horse owners that horses are vaccinated before transport to the U.S.; there are no requirements for core vaccines before importation,” says DeNotta, who at the time of the case chaired the American Association of Equine Practitioners’ (AAEP) Infectious Disease Committee (IDC)—a specialized group tasked with monitoring, updating, and evaluating infectious diseases affecting horses.
“The diseases we vaccinate for are not inconsequential,” she adds. “Many of them are fatal in a high percentage of infected horses, and cases that do recover may never have an athletic career or be safe to ride.”
The case underscores two realities horse owners often overlook: Every horse needs protection against core diseases, and vaccination isn’t just a springtime task. Most vaccination plans include both spring vaccines and fall boosters based on a horse’s disease risk.
Sally DeNotta, DVM, PhD, Dipl. ACVIM,
is a clinical associate professor in large animal clinical sciences at the University of Florida’s College of Veterinary Medicine, in Gainesville. Originally from the rural Oregon coast, she received her DVM from Oregon State University, in Corvallis, and spent time in private practice in Oregon and Colorado before completing an internal medicine residency and PhD at Cornell University, in Ithaca, New York. She joined the UF faculty in 2018, where her clinical and research interests include neonatology, neurology, infectious disease, hemostatic therapies, and colic.
Rob Keene, DVM,
is a senior professional services veterinarian with Boehringer Ingelheim. He joined the Boehringer team in 2008 and provides technical and sales support to the company’s equine customers across the country and has more than 40 years of experience in practice and industry.
Keene received his undergraduate degree in animal science from Montana State University in 1980. He attended veterinary school at Colorado State University and graduated in 1983. He began his practice career in California in an exclusively equine practice, focusing on herd health, reproduction, and surgery. Since 1985 Keene has served as a consultant and technical services veterinarian for many veterinary and research companies. He serves on the advisory board for the equine sciences program at Montana State University and participated on various AAEP committees. Keene works primarily in the United States on behalf of Boehringer Ingelheim and lives in Three Forks, Montana, farming and ranching with his wife, Linda.
For many owners, vaccination starts with understanding which diseases every horse needs protection against and when boosters matter most.
Vaccination is one of the most efficient and effective methods of protecting horses against infectious disease. When a horse receives a vaccination, it stimulates his immune system, mimicking exposure to the infectious organism without causing disease.
“We hope that by vaccinating horses we can prevent, and get ahead of, any diseases that they may be exposed to,” says Dr. Rob Keene, senior professional services veterinarian with Boehringer Ingelheim, based in Three Forks, Montana. “And that’s in a very simplest form what vaccines do. Rather than them having to go through the pain and suffering (of) getting the disease, we can expose their immune system to these agents that they’re going to find in the environment, whether it’s from another horse or from the environment.”
Photo: Adobe Stock
When Horses Should Be Vaccinated
Spring + Boosters
Vaccinating horses is not a once-a-year event. It should occur in both spring and fall, and no one-size-fits-all approach exists beyond preventing the “core” diseases (those that are severe, highly fatal, and pose a risk to all horses). This is one reason to work with a veterinarian, who can tailor a vaccination plan to each horse, based on his needs, where he lives, and his level of risk. That plan includes the appropriate core and risk-based disease coverage, along with the initial vaccine series, booster schedule, and seasonal timing.
As for timing, veterinarians typically administer spring vaccines during wellness exams and then boosters in the fall.
“We defer to the AAEP vaccine recommendations,” says Keene. “A minimum of twice-a-year vaccination is what a lot of people recommend. And in certain situations more aggressive approaches are warranted.”
Don’t Overlook Fall
Horse owners might focus on spring vaccinations and overlook the importance of fall boosters. However, mosquito activity remains strong through late fall months (and even year-round) in some regions. So, horses like the one in the earlier example can remain at risk for mosquito-borne diseases and other infectious pathogens throughout the year. After the heat of the summer, competitions, sales, and other events can increase horse movement and commingling, raising the risk of respiratory disease.
“Most of these respiratory diseases, like influenza, EHV-1, and EHV-4, are seen in the fall and winter months,” says Keene. “So are we best vaccinating that horse in March or April and expecting it to be protected until December? Probably not. That’s where fall comes in. We have all these diseases that are more common in the winter months, and we need to get ahead of those diseases. Vaccinating in the fall, especially for these risk-based diseases, is very, very warranted.”
“Vaccinating in the fall, especially for these risk-based diseases, is very, very warranted.”
Owners need to remember to vaccinate not only their adult horses but also their youngsters in the fall. Foals receive an initial series of three vaccine doses against each disease three to four weeks apart to prime their immune systems and ready them for annual or semiannual boosters for the rest of their lives. Foals born in the spring start their primary series around 4 to 5 months old, meaning they get their first vaccines in the summer and fall.
“A common error is to assume that foals finishing their primary series in the beginning of their yearling year are protected until their 2-year-old year,” says DeNotta. “Young horses have less-robust immunity than adult horses, who have received boosters for several years. Yearlings need boosters to bolster the immunity they gained from their primary vaccine series as foals. It is not uncommon to see cases of EEE in the summer or fall of the yearling year because they did not receive that spring booster. The take-home is that foals that finish their primary series still need to complete both their spring and fall vaccines of their yearling year.”
STORY CONTINUES BELOW
Risk-Assessment Q&A
When scheduling vaccinations, it’s helpful for horse owners to come prepared with answers to general risk-assessment subjects. Understanding where the horse lives, the owner’s riding goals with the horse, and the horse’s overall health and medical history will help the veterinarian make recommendations.
It’s important to note that vaccines reduce risk but do not guarantee full protection from disease. Additionally, vaccines do not provide immediate protection. Vaccines and boosters should be given, ideally, at least 14 days before likely exposure (at an event or before traveling). Ask any questions you have, including costs if that is a concern, and complete the information below to help your veterinarian develop a vaccine strategy for your individual horse.
About the horse:
- Age
- Breed
- Sex
- Their job: for example, competition, breeding, companion
- Upcoming events such as shows and travel
Health and vaccine history:
- Nutrition and general management (think parasite control)
- Any potential stressors or preexisting conditions, including genetic conditions such as immune-mediated myopathy in Quarter Horses
- Whether the horse has received vaccines or needs a primary series
- The vaccines received
- Date of last boosters administered
- Any prior adverse reactions
Anticipated exposure:
- If the horse currently travels or will be traveling
- Biosecurity strategies in place
- Level of exposure to or commingling with others
- Travel history of herd mates
Environmental factors:
- Home barn location
- Seasonal farm location (i.e., a farm in Florida where the horse competes over the winter)
- Average herd size
- Housing/turnout environment
- Local insect exposure and general conditions
Photo: Courtesy Equine Network
Disease Costs Money
Vaccination provides an effective way to prevent many infectious diseases. “Our horses are very expensive, and we want them to live a long, healthy, productive life,” Keene says. “We want to protect them against various diseases that are potentially life-threatening and can take us out of the game, whether we’re performing, trail riding, or just looking at our horse in the backyard.”
Without vaccination, horses are more susceptible to diseases, and care can become expensive. “Horses being treated for communicable disease need to be placed in isolation to prevent further transmission, which can be quite costly,” says DeNotta, noting that in addition to medications specific to the disease at hand, many horses need supportive care that could include anti-inflammatory drugs, intravenous (IV) fluids, and nutritional support at a minimum. More serious cases, such as horses suffering from signs of neurologic disease, might require a sling if unable to stand. The level of care for infectious disease can cost thousands of dollars—exponentially more than the vaccines used to prevent them in the first place.
“For some of these diseases, the true survival rate is difficult to discern because many horses are euthanized because the cost of care is so high,” DeNotta adds. “It’s sad to think that most of these cases wouldn’t have occurred had the horse been properly vaccinated.”
Equine Disease Outbreaks
Many of us have seen the catastrophic impact of equine disease outbreaks. The risk is great. For example, in November 2025 veterinarians tracked an outbreak of the deadly neurologic form of equine herpesvirus-1 (EHV-1) that originated at the Women’s Professional Rodeo Association (WPRA) World Finals and Elite Barrel Race event in Waco, Texas.
Veterinarians confirmed EHV-1 infection in 60 horses (although the impact was much wider than that):1
EHM (equine herpesvirus myeloencephalopathy, meaning infected horses had neurologic signs) cases—PCR (polymerase chain reaction test) positive:
47
EHV-1 cases—PCR positive, respiratory signs and/or fever but no neurologic signs:
9
EHV-1—PCR positive, no clinical signs:
4
Note the timing: Important events would occur within the following month—the National Finals Rodeo (NFR) and the World Series of Team Roping (WSTR), in Las Vegas, Nevada.
Keene says this situation likely prompted owners to vaccinate or booster their horses against the rising risk of disease. “There are 8,000 horses at the WSTR, and we identified zero positive nasal swabs, and that’s pretty remarkable after 15 years (of testing),” he explains. “Most of the diseases that we had diagnosed previously (at WSTRs) were preventable with vaccination.”
This remains a remarkable success story for the industry, following such an outbreak event.
“It’s just really important to be as strategic as you can to immunize and try to get ahead of these high-stress events where you’re going to have hundreds or thousands of horses commingling,” says Keene. “The chance of disease transmission is very, very high in a very, very stressful situation. All the stars are aligning, and usually there’s quite a bit of disease issues going on at those kind of events.”
Ultimately, in preventing outbreaks Keene recommends horse owners “get above the fray” by:
- Working closely with a veterinarian
- Implementing an aggressive booster program prior to events
- Boostering vaccines in the fall ahead of going to events and disease exposure
Photo: Adobe Stock
Core Vaccinations: Protection Every Horse Needs
According to the AAEP, the American Veterinary Medical Association (AVMA) defines core vaccinations as those “that protect from diseases that are endemic to a region, those with potential public health significance, required by law, virulent/highly infectious, and/or those posing a risk of severe disease. Core vaccines have clearly demonstrated efficacy and safety and thus exhibit a high enough level of patient benefit and low enough level of risk to justify their use in the majority of patients.”
In its vaccination guidelines the AAEP lists five core vaccinations against the following diseases: Eastern equine encephalomyelitis (EEE) and Western equine encephalomyelitis (WEE), rabies, tetanus, and West Nile virus. All horses can be exposed to pathogens causing the five core equine diseases.
Emily Berryhill, DVM, Dipl. ACVIM,
is an associate professor in the Department of Medicine and Epidemiology at the University of California, Davis, Weill School of Veterinary Medicine. She earned her DVM from UC Davis, where she also completed a large animal internal medicine residency. Her research focuses on equine oncology and endocrinology, with a special interest in providing veterinary care to donkeys. Berryhill loves all equids, but her No. 1 equine love will always be the cow horse.
Eastern equine encephalomyelitis (EEE) and Western equine encephalomyelitis (WEE)
These mosquito-borne viral diseases cause inflammation of the brain and spinal cord, resulting in debilitating neurologic signs; EEE mortality rates range up to 90%.2
West Nile virus
This potentially fatal mosquito-borne disease causes central nervous system inflammation, resulting in neurologic signs.
“I think the importance of equine vaccination is twofold,” says Dr. Emily Berryhill, associate professor of medicine and epidemiology at the University of California, Davis, Weill School of Veterinary Medicine. “To protect the individual from potentially life-threatening diseases and, also, to protect the herd, (horses at) show facilities, and anyplace horses are commingling. By protecting the individual, we also hope to provide herd immunity and reduce disease risk.”
Rabies
Caused by a virus spread via the saliva of infected animals, rabies travels through the peripheral nerves, up the spinal cord, and into the brain, causing neurologic dysfunction, and is invariably fatal.3
Tetanus
A costly and potentially fatal bacterial disease caused by Clostridium tetani (found in the soil), tetanus manifests as violent muscle spasms, hyperreflexive (exaggerated involuntary) responses, and “lockjaw.”
Photo: Getty Images
Risk-Based Vaccination: Tailored to the Individual Horse
Unlike core equine diseases that threaten every horse, horses at increased likelihood for risk-based diseases include the following:
- Younger horses
- Senior horses
- Broodmares
- Those residing in boarding barns
- Those traveling off property and competing
- Those stabling with horses that travel
- Those living where there is a regional-based threat of disease
Common risk-based threats horses can be exposed to include the following:
Equine herpesvirus (EHV-1 and EHV-4) As mentioned earlier, this critical respiratory infection could also cause abortion, nonviable foals, and neurologic signs.
Equine influenza This respiratory disease spreads by aerosol transmission (droplets from coughing or sneezing) from horse to horse.
Strangles This highly contagious upper respiratory disease is caused by the bacterium Streptococcus equi ssp equi (S. equi). Classic signs include a nasal discharge, swelling/abscessation of the lymph nodes of the head and neck, fever, coughing, difficulty eating, and lethargy. It is spread horse to horse and via fomites (objects, hands, body parts, etc.).
Potomac horse fever This late-spring and early-fall risk presents with mild colic, fever, severe diarrhea, depression, and loss of appetite. It can also progress to complications such as abortion in pregnant mares and laminitis.
Botulism This potentially fatal disease is caused by a neurotoxin produced by the bacterium Clostridium botulinum, which targets nerve endings.
Rotavirus (for broodmares) This highly contagious condition causes diarrhea in foals
The AAEP Equine Vaccination Guidelines provide a consensus to equine vaccination—what kind, which one, and how many to administer.
AAEP Equine Vaccination Guidelines*
| Core Vaccines | Which Horses | Timing |
| EEE/WEE | Every horse | One time annually following initial two-dose series (second dose four to six weeks after first dose)
Booster at six-month intervals for horses under 5 and those in endemic regions |
| WNV | Every horse | One time annually following initial two-dose series (second dose four to six weeks after first dose)
Booster at six-month intervals in endemic regions |
| Rabies | Every horse | One time annually |
| Tetanus | Every horse | One time annually following initial two-dose series (second dose four to six weeks after first dose)
|
| Risk-based vaccines | Which Horses | Timing |
| Equine influenza | Horses under 5 and those in contact with other horses | Six-month revaccination intervals unless horse is at low risk of exposure, then once a year annually |
| Equine herpesvirus (EHV-1 and EHV-4) | Horses on breeding farms, in contact with broodmares, horses under 5, and performance horses | One time annually after initial two- or three-dose series three to four weeks apart Booster six-month intervals for horses under 5, those on breeding farms or in contact with broodmares, and performance horses |
| Strangles | Horses residing on farms with endemic risk and those in contact with horses of unknown history | Six- to 12-month intervals depending on risk, following initial two- or three-dose series at two- to three-week intervals |
| Potomac horse fever | Horses kept near natural water sources or in irrigated pastures | Semiannual or annual booster following two-dose series, with second dose three to four weeks after first dose |
| Botulism | Broodmares in endemic areas and horses consuming round bales, haylage, or silage | One time annually following three-dose series, with second dose four weeks after first, and third dose four weeks after second dose |
| Rotavirus | Broodmares | Three-dose series, with first dose at eight months gestation, second and third doses at four-week intervals thereafter |
* Refer to label indications and work with your veterinarian to develop an equine vaccine strategy for your horse.
STORY CONTINUES BELOW
Photo: Getty Images
Vaccination and Biosecurity Work Together
Vaccinations play an important role in reducing disease risk, but they cannot eliminate exposure. “I’ve got some great photographs of 150 horses tied to the same rail at a large team roping event,” says Keene. “Be antisocial; park your horse elsewhere.” In addition, help limit exposure by keeping in mind these biosecurity best practices.
“I’ve got some great photographs of 150 horses tied to the same rail at a large team roping event. Be antisocial; park your horse elsewhere.”
Administer vaccines two weeks or more before travel to allow the immune system to build protective antibodies.
Prevent nose-to-nose contact with other horses.
Avoid sharing buckets and equipment among horses.
Keep horses away from others in the warm-up arena; avoid large groups.
Don’t let horses drink from shared water sources, directly from the hose, or dip the hose into their water buckets.
Should a disease outbreak occur, remember pathogens spread via fomites—hands, surfaces, and clothing.
Isolate and quarantine new arrivals or returning horses for at least two to three weeks.
Observe horses closely for any signs of disease, such as coughing, and ensure they have a good appetite.
If horses returning from off the farm go off feed, quickly check for fever; 99.5-101.5 F is the normal temperature for a horse.
Photo: Getty Images
Final Thoughts: A Story of Recovery
Berryhill, who has seen her share of horses combating both core and risk-based diseases, says “If we provide the support they need, they can really amaze you with their ability to survive and overcome.”
She recalls one of her favorite patients—a 2-year-old bay Thoroughbred filly. A budding racehorse, the filly developed clinical signs of tetanus to the point she was unable to stand. (She had been vaccinated, but did not receive the required primary series to generate an appropriate protective response.)
“She hated the sling and hated her legs wrapped,” Berryhill says. “She couldn’t eat for a while and needed so much TLC from everybody and financial resources from her owner. Her owner was just like her horse—super tough—and as long as she wasn’t ready to quit, we weren’t ready to quit. The filly has since gone on to win races, and she’s still racing.”
When the consequences can be life-threatening, vaccination is a risk few owners can afford to overlook. As Keene says, “It’s important that we vaccinate against all these various things that may be life-threatening.”
Sponsor Message
Boehringer Ingelheim vaccines offer exceptional protection. With more than 17 million doses administered, Boehringer Ingelheim has proven its expertise in the development and production of high quality, efficacious equine vaccines. The Boehringer line of VETERA® vaccines offers current and effective disease protection, comprehensive and flexible options, cutting-edge vaccine technology, a vaccine assurance program and a veterinary technical service team for support.
VETERA is the only equine vaccine portfolio that is safe in pregnant mares and horses 4 months of age and older. The portfolio protects against core and risk-based diseases and offers protection against both Clade 1 and Clade 2 strains of equine influenza.
With multiple combinations, Boehringer Ingelheim can offer the right protection for every horse.
Boehringer Ingelheim provides innovation for preventing and treating diseases in animals. The company offers a wide range of vaccines, parasite control products and medicines for pets, horses and livestock to veterinarians, animal owners, farmers, and governments. As a leader in animal health, Boehringer Ingelheim values that the health of humans and animals is deeply connected and strives to make a difference for people, animals, and society. Learn more about VETERA here. For equine health educational articles, click here.
VETERA® is a registered trademark of Boehringer Ingelheim Vetmedica GmbH, used under license.
US-EQU-0202-2026
About the Author
A.E. Robinson has been starstruck with horses since she was given a pony named Sparkler at age 3. With a journalism degree from Oklahoma State University, her magazine-editorial and marketing career centers around the animal health industry. From writing educational pieces that help horse owners to including vaccines and more—every aspect of her career has been driven to help the horses, livestock, and pets we love.
Editorial Director: Stephanie L. Church
Managing Editor: Stephanie J. Ruff
Digital Managing Editor: Haylie Pfeffer
Art Director: Claudia Summers
Web Producer: Jennifer Whittle