Vaccination Questions Answered!

Spring vaccine season is approaching and with it comes the quandary of what vaccines does your horse actually need?  Here is a quick vaccine guide and the answers to your most common questions:

Is there a standard vaccine protocol for every horse?
No!  We tailor vaccines to the individual horse/barn.  A horse’s location, use, lifestyle and age all play a role in what vaccines are recommended.

Are there any blood tests to see if your horse needs a particular vaccine? 

No!   According to the American Association of Equine Practitioners “standardized tests and protective levels of immunity have not been identified for most diseases.”  The only blood test related to vaccines that is most commonly used is called a Strep Titer.  If your horse is receiving their first Strep (Strangles) vaccine ever, or the first one in a long time, a Strep Titer helps us determine their level of risk for adverse reactions.

What is the benefit of giving individual vaccines versus one vaccine for everything?

Administering vaccines for individual diseases allows us to tailor your horse’s vaccine program.  It also benefits the horse by allowing their immune system time to react properly to each vaccine instead of being overwhelmed by stimulus.  There is research which shows that a horse’s immune system makes a higher antibody level after an individual vaccine rather than combination vaccines.   In addition, it allows better tracking of what your horse has been vaccinated against.  For instance, we see many horses whose vaccine history includes that they got a “5-way” or “6-way” vaccine but the owner does not actually know what diseases that vaccine includes.

Does your older horse still need vaccines?

Yes!  Age and certain diseases such as Cushing’s (PPID) can suppress their immune system making vaccines even more important.

My horse doesn’t go anywhere, does he still need vaccines?

Yes!  Even if your horse lives alone and does not leave your backyard there are some vaccines that are still necessary.  Just because your horse stays at home, doesn’t mean that insects won’t come to them bringing diseases such as West Nile, Equine Encephalitis, and Potomac Horse Fever.   Your horse also has the potential to have animal visitors (skunks, raccoons, foxes) which could bring rabies onto your property. There are also vaccines which protect against organisms found in the environment such as Tetanus and Botulism.

I never hear about the disease anymore, does my horse really need to be vaccinated against it?

Yes!  The diseases are still present and still occur.  The reason you don’t hear about them often is because the majority of the horse population is vaccinated against them.  If we stopped vaccinating, the diseases would become very common again.  You can go to to see some information on disease occurrence in horses.   This site will not show every occurrence of each disease as they are not always reported, but it does help confirm that the diseases still occur naturally in the horse population.

Is vaccine protection immediate?

No!   The immune system takes time to respond to vaccines and to build up its defenses.  If a horse has never been vaccinated against a particular disease, multiple vaccines at set intervals will be necessary to establish protective immunity.  If a horse has been regularly vaccinated against a particular disease it should be given again at least 2 weeks before anticipated exposure.  Boosters will need to be repeated annually or biannually to keep up the horse’s immune status.

Why are some vaccines intramuscular while others are intranasal?

There are primarily 2 types of equine vaccines.  (1) Modified-live vaccines which stimulate the immune system by presenting a modified disease-causing microbe (bacteria or virus).  (2) Inactivated vaccines which stimulate the immune system by presenting a killed microbe or a part of an inactivated microbe to stimulate the immune system.    Most equine vaccines are inactivated.

Intramuscular vaccines are usually inactivated.  Intranasal are typically Modified-live.   Strangles and Influenza vaccines come either as a killed vaccine to be administered in the muscle or a Modified-live vaccine which is given intranasally.  The benefit to an intranasal vaccine is that it stimulates local immunity.  This benefits the horse by making sure that the tissues that would be first exposed to the disease are the tissues that have the strongest immunity to it.  The downside is that some horses do not behave well for intranasal vaccines, making physical safety a concern.

Intranasal Flu and Strangles vaccines are typically recommended for horses that show or travel frequently, board where other horses are showing/traveling or live where there is a high turnover in the equine population, and for horses who do not tolerate the intramuscular forms of these vaccines.

There is also some evidence that the intranasal variety of the flu vaccine may also help induce some immunity against other respiratory diseases.

Intranasal vaccines are not recommended for broodmares.  Since they create a local immunity in the nasal passages and upper respiratory tract this protection is not passed to the foal in colostrum.  The antibodies made following intramuscular injection will be passed through the colostrum to the foal.

 Why should a veterinarian administer my horse’s vaccines?

There are many reasons for this, including: 

  • Veterinarians are equipped to handle vaccine reactions.
  • We can help you tailor a program to your horse’s specific needs.
  • We can ensure that the vaccines are handled properly.
  • Rabies vaccines are not recognized unless administered by a Veterinarian.


Which vaccines should be considered in Virginia?


All horses are at risk of this typically fatal disease.  Vaccination against tetanus is considered a core vaccine and is indicated for all horses.  Tetanus is not contagious from horse to horse but the bacteria which causes the disease is found in soil and feces.  The organism can survive in the environment for years, resulting in an ever-present risk of exposure through wounds, surgical incisions or even a newborn foal’s umbilicus.    The severity of the wound does not predict the risk for tetanus.  All horses should be vaccinated annually and the vaccine should be repeated sooner if they have a wound or are undergoing surgery.

Eastern and Western Equine Encephalitis: 

EEE and WEE are viral diseases transmitted by mosquitoes and potentially other bloodsucking insects.  EEE has a mortality rate of approximately 90%.  WEE has a lower mortality rate,  but approximately 50% of infected horses will die from the disease.    There have been recent horse cases of EEE along the east coast.  In addition, surveillance programs still identify both of these viruses in our mosquito and bird population.   Currently, we recommend vaccinating against EEE/WEE annually.  In areas with high mosquito populations or when cases occur in the equine population, the frequency of vaccination is often increased.


Rabies is a fatal disease which occurs infrequently in horses.  In addition, it has considerable public health significance.  The Rabies vaccine should be considered a must-have vaccine and is should be administered annually.  Exposure typically occurs through the bite of an infected animal (raccoon, skunk, fox, or bat).  A bite usually occurs on the muzzle or lower limbs and once the virus enters the body in migrates to the brain causing fatal encephalitis.

West Nile:

West Nile is another cause of viral encephalitis in horses.  According to the AAEP, horses represent almost 97% of all reported non-human mammalian cases of West Nile Viral disease.  The virus has been identified in each of the continental United States.  The virus is transmitted by mosquitoes.  Horses and humans are considered dead-end hosts, meaning that the virus is not directly contagious from horse to horse or horse to human.   Approximately 30% of infected horses will die and approximately 40% of the survivors will exhibit symptoms more than 6 months after the initial infection.   This vaccine is recommended annually or biannually for susceptible populations.

Potomac Horse Fever:

Potomac Horse fever is a potentially fatal bacterial disease and is often found on properties with small creeks or streams.  It has been associated with the ingestion of insects that are carrying the bacteria.  Clinical signs of Potomac Horse Fever may include fever, mild to severe diarrhea, laminitis, and colic.  The disease occurs seasonally from spring to early fall with most cases occurring in July, August, and September.  If Potomac Horse Fever occurs on a farm or in a particular geographic area it is likely that cases will occur in future years.  The vaccine is recommended every 6 months and in some cases, more frequently.


Equine Influenza is one of the most common infectious diseases of the respiratory tract in horses.  Sporadic outbreaks occur after the introduction of an infected horse to an unprotected group of horses.  Young horses and horses that travel or show are at the most risk.  Equine influenza is highly contagious and is spread through coughing.  Some infected horses can show no symptoms, but can still spread the infection.   Vaccination should be done at least every 6 months.   If your horse shows, you may need to follow the USEF vaccination rule found here:

There are multiple types of equine influenza vaccine available.  The inactivated vaccine, which is administered in the muscle, has been shown to be efficacious in protecting from clinical disease and viral shedding.    The Modified-live (MLV) equine influenza vaccine is administered intranasally.   The intranasal (MLV) vaccine is recommended for horses that are showing and traveling or live in a barn with high turnover.   There is some anecdotal evidence that the intranasal influenza vaccine may help protect against other respiratory viruses.

Rhinopneumonitis (Equine Herpesvirus):

Equine herpesvirus type 1 (EHV-1) and equine herpesvirus type 4 (EHV-4) infect the respiratory tract causing mild to severe respiratory signs like fever, lethargy, anorexia, nasal discharge, cough, and swelling of the lymph nodes.  Similar other herpes viruses, they may establish a latent/hidden infection in horses allowing them to become carriers.  These horses may experience reactivation of the virus in times of stress allowing them to shed the virus, therefore exposing others to the disease.

Most mature horses may not show signs of infection when exposed but they can easily become carriers and can put other horses at risk.  Vaccination is recommended for horses at risk including young horses, horses stressed by showing or traveling as well as horses who share barns with horses that do.

Both of these viruses have been associated with neurologic disease.  There is no vaccine available to protect against the neurological form of the virus.  Keeping horses vaccinated against the respiratory form of the virus can help reduce the incidence of the neurological variant.

There are 2 forms of vaccine available.  The inactivated vaccine is usually found in combination with the inactivated influenza vaccine.  The modified-live vaccine just protects against rhinopneumonitis and is given intramuscularly.  Vaccination against equine herpesvirus types 1 and 4 (rhinopneumonitis) is recommended at least twice each year.  If your horse shows, make sure to follow the FEI rules just like for Equine Influenza


Botulism in horses is usually one of three syndromes:  Wound botulism (from contamination of infected wounds), Shaker Foal Syndrome (toxin from ingested spores), or Forage poisoning (ingestion of the toxin produced in decaying plant material or animal carcass remnants present in feed/hay.)

The Botulinum toxin is the most potent biological toxin known.  It causes muscle weakness progressing to paralysis, inability to swallow, difficulty breathing, and often leads to death.  The available vaccine protects against the B toxin which is responsible for more than 85% of the equine botulism cases in the United States. Most mature horses may not show signs of infection when exposed but they can easily become carriers and can put other horses at risk.  Vaccination is recommended for horses in the mid-Atlantic states.


Lyme disease causes a wide variety of symptoms in horses including fever, shifting lameness, and a change in attitude or overall comfort.  There is no vaccine labeled to prevent Lyme disease in horses.  The canine (dog) version of the vaccine has been successfully used in horses.  After the initial 3 shot series, this vaccine is given twice each year.


Strangles is a bacterial disease caused by Streptococcus equi subspecies equi.  Horses of any age can be affected.  Symptoms can include fever, swollen lymph nodes, and often anorexia.   Some horses can show no symptoms but instead become carriers of the bacteria and a source of infection to other horses.  The bacteria is spread through direct contact with an infected horse, a carrier or by contact with surfaces contaminated with nasal discharge from an infected horse.   Water troughs, feed bins, grooming tools, and humans often become fomites (carriers of the bacteria).   Vaccination in susceptible horses is done once or twice yearly.  There are two types of vaccines available, a killed vaccine that is given in the muscle and a Modified-live (MLV) vaccine that is given intranasally.

Strangles can be associated with a potentially fatal syndrome called purpura hemmorhagica which is a generalized vasculitis (inflammation of blood vessels) leading to hives, swelling of limbs, facial swelling, sloughing of tissue, and possibly death.  This syndrome has been associated with natural infection as well as vaccination against strangles.  A blood test called a Strep titer can see if you horses antibody level is low enough to safely vaccinate.

Vaccines against other diseases like Equine Rhinitis Virus (ERAV), Leptospirosis are available too.    There is even a vaccine that can help protect against rattlesnake bites.