Equine Vaccines: Essential Knowledge for Horse Owners

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It’s that time of year, vaccine season! There are so many different options out there, it’s easy to get confused as to what is best for you and your horse. In this blog we will cover:

  • How do vaccines work?
  • Do my horses need vaccines every year?
  • Which vaccines do my horses need?
  • The core vaccines
  • The risk based vaccines
  • Combination vaccines
  • When can I schedule a vaccine appointment?


How do vaccines work?

Vaccines introduce a very small, modified portion of a disease causing organism to the body. This is not enough to cause illness, but will train the body’s natural immune system to recognize the disease and be able to fight it off if ever naturally exposed. This can prevent serious illness and possible death from these diseases. 


Do my horses need vaccines every year?

The protection offered by vaccines does not last forever. Research has shown that the natural immunity stimulated will wane over time. For this reason, annual boosters are recommended to ensure your horse has the best protection possible. 


Which vaccines do my horses need?

There are many vaccines available, but every horses’ needs are different. For this reason we separate the vaccines into the “core” vaccines, which every horse will need each year, and the “risk based” vaccines, which are variable based on the lifestyle and management. 


The Core Vaccines 

The following vaccines are considered essential for every horse every year for the following reasons:

  1. The horse can be exposed without traveling or ever interacting with another horse
  2. The disease has a high chance of causing death if exposure occurs without the protection of vaccination 
  3. The vaccine offers a high level of protection 
  4. The vaccine is very safe with minimal risk of adverse reaction.
  • Tetanus Toxoid: Tetanus is a disease caused by a common bacteria found in soil, Clostridium tetani. This bacteria creates a potent neurotoxin and can enter the body though any wound. The wounds can be very small and difficult to identify (sometimes occurring in the mouth). Horses are very sensitive to the tetanus neurotoxin and the disease is easily contracted in unvaccinated horses. Tetanus causes spasm of the muscles which can lead to paralysis and an inability to breathe. Treatments are available for very early cases, but it is very often a fatal disease. Vaccination with a tetanus toxoid vaccine is an incredibly safe, effective and cheap way to prevent this deadly disease. (Note: A separate tetanus vaccine known as “tetanus antitoxin” is also available. This is a product designed to help prevent tetanus in unvaccinated animals after potential exposure. This product is difficult to obtain due to production issues and it also has potential for severe, life threatening, reactions. For this reason the tetanus antitoxin vaccine should be considered in case of emergencies, and should not replace a routine tetanus toxoid vaccine program.) 

Here is a video showing a horse with early clinical signs of tetanus:


  • Rabies: Rabies is a disease that while uncommon in horses, is always fatal if contracted. There is also potential for exposure to humans from an infected horse, which makes it a significant public health risk. Rabies is transmitted to horses from a bite from infected wildlife. Many boarding barns and horse events will require proof of rabies vaccination. Only vaccines administered by a veterinarian will come with a rabies certificate, which is considered proof of vaccination. 

Here is a video detailing the clinical signs of rabies in horses:

  • West Nile Virus (WNV): West Nile Virus is carried by mosquitoes and all horses are susceptible to the disease. Approximately 30% of unvaccinated horses will die after infection with WNV and a further 40% will have lasting neurologic damage. The vaccine is very effective at preventing infection with this disease. 

Here is a video of typical symptoms of WNV infection:

  • Eastern/Western Equine Encephalomyelitis (EEE/WEE): EEE and WEE are both viruses transmitted by mosquitoes. There is also a related Venezuelan Equine Encephalomyelitis virus (VEE) but it is classified as an exotic disease and only horses living on the southern US border are considered at risk. (This is not a disease of concern in Ohio)  EEE/WEE causes neurologic symptoms and is often fatal. The vaccine is very effective at preventing infection.    

Rarely, humans can also become infected with WNV or EEE.  In order for this to happen they must be bitten by an infected mosquito. Horses are considered “dead end hosts” for these diseases, meaning while they can become infected with the disease they can not transmit it to other animals. 


Risk Based Vaccines 

There are many diseases that have available vaccines, but not all of them are appropriate or required for your individual horse's lifestyle. There are several things that will influence if you may benefit from these vaccines:

  1. Your horse competes at shows with specific vaccine requirements
  2. Your horse travels off farm and is exposed to other horses 
  3. Your horse is stabled at a farm where outside horses visit frequently to train or show
  4. Your horse is exposed to other horses that leave the farm to show or group ride
  5. Your horse has access to a pond or stream in or near their pasture
  6. Your horse is fed round bales
  7. Your horse is pregnant

The following vaccines are ones that we offer in our practice that may be suitable for you. 

  • Equine Influenza/Herpes 1/4(Rhinopneumonitis): This is a common combination vaccine known as “Flu/Rhino”. These are contagious upper respiratory respiratory viruses that are spread by contact with other infected horses. The infected horses may be acting sick or they may be apparently healthy and shedding the virus. This vaccine is often required for sanctioned shows (such as USEF) and is recommended for any horses that will be exposed to horses outside of their normal herd. 

At Carrollton Equine we carry both the injectable Flu/Rhino (Vetera 2xp) as well as an intranasal option (Calvenza). In order to use the Calvenza as an intranasal option there needs to be two previous doses of the vaccine in the muscle.

 Flu/Rhino vaccines must be administered by a veterinarian in order to have a certificate required for showing.    

Here is a good article about equine flu/rhino infection and the vaccine requirements for USEF shows:

Equine Flu: What You Need to Know

Some strains of herpes virus can cause neurologic disease. SInce this is thought to be due to a mutation of the herpes virus, there is no targeted vaccine to prevent the neurologic strain.   

  • Equine Herpesvirus 1 (Rhinopneumonitis for pregnant mares): Broodmares should be given a Rhino vaccine at 5, 7 and 9 months of pregnancy. EHV-1 can cause respiratory infection in young horses, but it can also cause abortion in pregnant mares. Here is a summary of how to vaccinate your broodmares:

Vaccinating Your Pregnant Mares- Haygard Equine Medical Institute 

  • Potomac Horse Fever (PHF): PHF is a gastrointestinal disease caused by the bacteria Neorickettsia risticii. This bacteria lives inside aquatic insects (such as snails and mayflies) and horses become infected when they inadvertently ingest the insects while grazing. Once infected, horses can experience fever, diarrhea and laminitis. The clinical signs can range from mild to severe enough to require hospitalization and possibly resulting in death.  

There are some locations of the country that are considered “hot beds” of the disease with many reported cases each year. Northeast Ohio is not such a place, but it does not mean the disease is not present in the region. Vaccination does not always prevent infection, but it has been shown to significantly decrease the severity of the disease. If your horses have access to a pond or slow moving water in their pasture, they are at risk for ingesting the aquatic insects and vaccination should be considered. Even if there is no water in their pasture, horses that travel and may be exposed to different pastures throughout the year should also be considered for vaccination. 

PHF is a seasonal disease with most cases occurring in the late summer and early fall. For this reason, it is important to time the vaccination schedule so that the horse has peak immunity during those times of year. We do not recommend vaccinating for PHF any earlier than May for this reason. 

Here is a great article with more information about Potomac Horse Fever:

Potomac Horse Fever: AAEP

  • Strangles (Strep. Equi equi) : Strangles is a highly contagious infectious disease that is a major concern for most horse owners. Horses infected with strangles will develop a high fever, nasal discharge, cough and swelling in the lymph nodes under the jaw and in the throat. Most horses recover without incident but there are potentially serious complications such as internal abscess formation or severe systemic inflammatory reaction known as “purpura.” The disease is transmitted through contact with an infected horse or through items that have been in contact with an infected horse (boots, jackets, brushes etc.). The reason strangles is so easily transmitted between barns is because there are some horses that can shed the bacteria and be contagious to others while not appearing sick themselves. 

There is a strangles vaccine available which can be used to help reduce the likelihood of a farm outbreak. The vaccine is administered intranasally and is “modified live,” meaning it still has a capacity to cause mild pathology. 

To learn more about strangles, here is a great video that goes into detail about the disease:

**If you are interested in vaccinating your horse against strangles, please contact us to discuss it with one of our doctors. There is a potential for a serious vaccine reaction for horses that have previously been exposed to the disease and still have a high antibody titer. A blood test is available to help determine your horse’s risk of reaction. 

  • Botulism:  Botulism is caused by neurotoxin that the horse ingests from contaminated feed. It produces a flaccid paralysis that causes weakness, trembling and an inability to stand. Feed becomes contaminated from either improper preparation of roundbales or animal caracasses (mice, birds, rabbits) in feed or hay. Botulism is fatal if not caught very early and the vaccine is effective at preventing disease.
  • Lyme:  Lyme disease is carried by ticks and can cause neuromuscular disease. There is no FDA approved Lyme vaccine for horses. However, studies have shown that the dog vaccine is safe and does provide an antibody response in horses. 

For more information on Lyme disease in horses, check out this article from Cornell University:

Lyme Disease in Horses


What combination vaccines are available?

Each vaccine comes as its own product, but you don’t have to make a million appointments to get your horse protected as there are several combination vaccines available. Here is what we carry at Carrollton Equine:

  • 4-way vaccine: This includes Tetanus, EEE/WEE and West Nile Virus. 
    • This plus a Rabies vaccine provides all of the “core” vaccines
  • 6-way vaccine: This includes everything in the 4-way (Tet/EEE/WEE/WNV) plus Flu/Rhino
    • This is a common vaccine for horses that show and need flu/rhino coverage
    • This can be given with a rabies in one visit 
    • This is the largest combination vaccine on the market 
  • Rabies & Potomac Horse Fever:This vaccine covers Rabies and PHF
    • Remember that PHF should not be given any earlier than May 

When can I schedule a vaccine appointment?

Vaccines are typically given in the spring as many of the diseases are transmitted by insects. Administering vaccines in the spring gives the immune system a boost to be fully protected when they are most likely to be exposed to the disease. For some horses that travel down South for the winter season, doing a second set of vaccines in the fall is sometimes recommended as they have a longer insect season. 

Vaccines can be given to healthy horses during visits for other procedures such as dentals, chiropractic adjustments or lameness exams. Vaccines should not be given to animals that are ill or will be on steroids at the time of vaccination (such as during a heaves flare or on the same visit as joint injections). 


Reach out today to schedule a vaccine appointment!


About The Author

Dr. Alyson Waring-Scott

MVB, cVMA, VSMT  |  Equine Veterinarian

I am an Equine Veterinarian at Carrollton Equine and enjoy all aspects of equine medicine. I am especially passionate about dentistry and ophthalmology, and have received advanced training in both of these areas. I am also certified in medical acupuncture and VSMT (chiropractic). 

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