What Vaccines Does My Horse Need and How Often?

By Dr Duncan Houston

If your horse missed their usual spring vaccinations, do not panic and do not wait until next spring. In most cases, the best time to catch up is as soon as your veterinarian confirms that your horse is healthy enough to be vaccinated.

The more important issue is not the month on the calendar. It is whether your horse is protected before the next likely exposure.

A horse’s vaccination plan should reflect where they live, which diseases occur locally, whether they travel, how often they mix with other horses, their age, breeding status, previous vaccination history and any history of vaccine reactions. There is no single vaccine schedule that is appropriate for every horse in every country.

Quick Answer

Most horses need a combination of geographically appropriate core vaccines and additional risk-based vaccines.

Under United States AAEP guidelines, the four core equine vaccines are tetanus, Eastern and Western equine encephalomyelitis, West Nile virus and rabies. Equine influenza, equine herpesvirus and strangles are commonly added when a horse travels, competes, boards, breeds or regularly encounters unfamiliar horses. Many adult boosters are given annually, but horses with ongoing exposure or prolonged mosquito seasons may require certain vaccines every six months. (AAEP)

These recommendations should not be copied blindly into another country. Australian horses, for example, have different disease risks and vaccine priorities, particularly tetanus, strangles and Hendra virus vaccination. (Australian Veterinary Association)

There Is No Universal Horse Vaccination Schedule

The AAEP specifically states that a standard vaccination program for all horses does not exist. A suitable plan requires an individual risk assessment rather than simply giving every available vaccine once a year. (AAEP)

Your veterinarian will consider:

• Your country, state and local disease risks

• Mosquito and other vector seasons

• Your horse’s age and previous vaccination history

• Whether your horse travels, competes or boards

• Contact with newly arrived or unfamiliar horses

• Whether your horse lives on a breeding property

• Pregnancy and expected foaling date

• Previous vaccine reactions

• Chronic disease or immunosuppressive medication

• Competition, transport and facility entry requirements

This is why two healthy horses living only a few kilometres apart may still need different vaccination schedules.

What Is the Difference Between Core and Risk-Based Vaccines?

Core vaccines protect against diseases considered severe enough, widespread enough, zoonotic enough or difficult enough to avoid that vaccination is recommended for essentially every horse within that geographical region.

Risk-based vaccines are selected after considering the individual horse’s likelihood of exposure and the consequences of infection.

The word “core” is geographical. A vaccine regarded as core in the United States may be unnecessary or unavailable in a country where the disease does not occur.

What Are the Core Horse Vaccines in the United States?

The AAEP identifies four core vaccines for horses in the United States.

Unvaccinated horses and horses with no reliable records may require a primary series rather than a single booster. The number of doses and spacing depend on the vaccine and product label. (AAEP)

Does an Isolated Horse Still Need Core Vaccines?

Yes, when those vaccines are considered core in the horse’s region.

Tetanus comes from environmental contamination of wounds. Mosquito-borne diseases do not require another horse to be nearby. Rabies exposure can occur through wildlife.

A horse living alone on a large property may have a lower risk of respiratory disease, but isolation does not remove environmental, vector-borne or wildlife-related risks.

What Vaccines Do Horses Need in Australia?

Australian owners should not automatically follow an American vaccination chart.

Australia remains free from rabies, equine influenza and Eastern and Western equine encephalomyelitis. Routine vaccination against those diseases is therefore not generally practised in the domestic Australian horse population. (Micor)

Australian vaccination priorities commonly include the following.

Tetanus

Tetanus vaccination is strongly recommended because the organism is present in the environment and even a relatively minor wound can provide a route of infection.

For a commonly used Australian tetanus vaccine, the primary course consists of two doses four to six weeks apart, followed by a booster 12 months later and then annual boosters. Product instructions must always be followed. (Zoetis)

Strangles

Strangles vaccination may be recommended for horses that compete, travel, live on breeding properties, board with other horses or are exposed to frequent horse movements.

The primary course and booster interval depend on the product used. Some Australian strangles products require a three-dose initial course, with annual boosters or six-monthly boosters for horses at greater risk. Vaccination works best as part of a wider biosecurity program, not as a replacement for quarantine and outbreak control. (Zoetis)

Hendra Virus

The Australian Veterinary Association recommends vaccination as the most effective way to reduce Hendra virus risk in horses and the associated risk to people. Hendra vaccination must be administered by a veterinarian and recorded in the central registry. (Australian Veterinary Association)

The current Equivac HeV schedule for horses four months of age and older is:

1. First vaccination

2. Second vaccination three to six weeks later

3. Third vaccination six months after the second dose

4. Further boosters every 12 months

Pregnant mares have additional timing precautions, so their vaccination dates should be planned with the attending veterinarian. (Zoetis)

Other Australian vaccines, including EHV-1 and EHV-4, rotavirus and Salmonella vaccines, may be appropriate for particular breeding, performance or export situations.

Which Risk-Based Vaccines Might My Horse Need?

Equine Influenza

Equine influenza is one of the most contagious respiratory diseases of horses in countries where it is present. It spreads through respiratory droplets and contaminated hands, clothing, trailers, tack, buckets and equipment.

Vaccination is particularly relevant for horses that:

• Attend shows, races, clinics or group rides

• Travel regularly

• Live at boarding or training facilities

• Mix with horses arriving from different properties

• Are young and entering training

• Must meet competition or venue vaccination rules

Under AAEP guidance, horses with ongoing exposure may be revaccinated every six months, while lower-risk horses may receive annual boosters. Some competitions or facilities require vaccination within the preceding six months. Australia is a notable exception because it remains free from equine influenza and does not routinely vaccinate its domestic horse population against it. (AAEP)

Equine Herpesvirus 1 and 4

EHV-1 and EHV-4 can cause respiratory disease. EHV-1 may also cause abortion, fatal neonatal disease and equine herpesvirus myeloencephalopathy, the neurological form of the disease.

Vaccination can reduce respiratory disease, nasal shedding and viraemia, but there is currently no licensed vaccine labelled to prevent neurological EHV-1 disease. Vaccination should therefore never be treated as a substitute for isolation, movement restrictions and outbreak biosecurity.

Six-monthly EHV vaccination may be recommended for:

• Horses younger than five years

• Horses on breeding farms

• Horses in contact with pregnant mares

• Horses at facilities with frequent movement on and off the property

• High-risk performance and show horses

Pregnant mares are commonly vaccinated against EHV-1 abortion during the fifth, seventh and ninth months of gestation using an appropriately labelled vaccine. A separate respiratory EHV booster may also be recommended four to six weeks before foaling.

Strangles

Strangles vaccination is most useful on properties where the disease is persistent or where a horse has a substantial risk of exposure.

It is not simply a vaccine that should be given to every horse during an active outbreak. Horses that have recently been exposed to strangles or previously developed purpura haemorrhagica require careful veterinary assessment before vaccination because exposure to Streptococcus equi antigens can occasionally trigger serious immune-mediated complications.

Other Risk-Based Vaccines

Depending on the country and the individual horse, additional vaccines may include:

• Botulism

• Leptospirosis

• Potomac horse fever

• Anthrax

• Equine viral arteritis

• Rotavirus vaccination for pregnant mares

• Venezuelan equine encephalomyelitis in relevant regions

• Region-specific snakebite vaccines

These vaccines should be selected because a genuine risk exists, not merely because the product is available.

When Is the Best Time of Year to Vaccinate a Horse?

The correct timing depends on when exposure is most likely.

Protection is not immediate. Some horses need two or three initial doses before meaningful protection develops, and the AAEP advises completing primary vaccination and boosters at least 14 days before anticipated exposure whenever possible. (AAEP)

Is It Too Late to Vaccinate My Horse?

Usually not.

Missing spring or autumn vaccination does not mean that the horse must remain unprotected until the following year. Your veterinarian can review the horse’s records and create an appropriate catch-up schedule.

The important question is how long the horse has been overdue.

A horse that is a few weeks late but has years of documented vaccination may be managed differently from a horse that has not been vaccinated for several years or whose vaccination history is unknown.

Do not assume that one injection immediately restores protection. Depending on the vaccine, product and length of the lapse, a new primary course may be recommended.

How Quickly Should an Overdue Horse Be Vaccinated?

Lower Immediate Risk

The horse is healthy, only slightly overdue, does not travel and has no anticipated exposure.

Action: Book a routine vaccination appointment and update the schedule.

Moderate Risk

The horse is several months overdue, boards with other horses or occasionally travels.

Action: Arrange vaccination promptly and avoid unnecessary exposure until the plan has been reviewed.

High Risk

The horse has no reliable vaccination history, regularly travels, lives at a high-turnover facility, is entering mosquito season or is due to attend an event.

Action: Contact your veterinarian now. A primary course or carefully timed catch-up schedule may be required.

Same-Day Veterinary Advice

Seek same-day advice when:

• The horse has sustained a penetrating wound and tetanus protection is uncertain

• Surgery is planned and tetanus vaccination is overdue

• The horse has been exposed to a confirmed infectious disease

• An outbreak is occurring on the property

• A pregnant mare has missed a time-sensitive vaccine

• The horse previously experienced a serious vaccine reaction

If the horse is already showing fever, coughing, nasal discharge, neurological signs or marked depression, isolate them from other horses and speak to a veterinarian before vaccination.

Can a Sick or Injured Horse Be Vaccinated?

Routine vaccination is generally intended for healthy horses.

Vaccination may need to be postponed when a horse has:

• A fever

• Active coughing or nasal discharge

• Significant lethargy or reduced appetite

• Colic or recent systemic illness

• An active inflammatory or immune-mediated condition

• Treatment with immunosuppressive medication

• A history of significant vaccine reactions

The decision is based on risk versus benefit. Chronic disease and pregnancy are not automatic reasons to avoid every vaccine, but the vaccine type and timing must be appropriate. (AAEP)

Injury is different from systemic illness. A wound is not automatically a reason to delay vaccination. A penetrating injury may make tetanus protection more urgent. A previously vaccinated horse may need a tetanus booster, while an unvaccinated horse may require both tetanus toxoid and short-term tetanus antitoxin under veterinary direction. (AAEP)

What Reactions Are Normal After Horse Vaccination?

Mild reactions can occur after vaccination and do not necessarily mean the horse should never be vaccinated again.

Expected short-lived signs can include:

• Mild soreness at the injection site

• A small local swelling

• Temporary stiffness

• Mild lethargy

• Reduced appetite

• A low-grade fever

Monitor the horse closely, provide access to water and avoid hard exercise if they appear sore or lethargic. Do not automatically administer anti-inflammatory medication before or after vaccination unless your veterinarian has advised it.

When Is a Vaccine Reaction an Emergency?

Contact a veterinarian immediately if your horse develops:

• Difficulty breathing

• Collapse or profound weakness

• Widespread hives

• Rapid facial, throat or limb swelling

• Severe or rapidly increasing injection-site swelling

• Colic

• Marked agitation or distress

• Ataxia or other neurological abnormalities

• A high or persistent fever

• Signs that continue to worsen rather than improve

Severe allergic reactions, including anaphylaxis, are uncommon but can be life-threatening. Purpura haemorrhagica may occur after natural strangles infection or vaccination and can cause marked swelling, haemorrhage and breathing difficulty. (AAEP)

Not every illness occurring after vaccination was necessarily caused by the vaccine. Coughing, significant nasal discharge, persistent colic or progressive neurological signs may indicate an unrelated or incubating disease and still require investigation.

What Should You Do If Your Horse Is Overdue?

1. Find the vaccination records. Look for the vaccine name, disease covered, date administered and previous booster history.

2. Check upcoming exposure. Tell your veterinarian about planned transport, competitions, breeding, new arrivals or changes in boarding arrangements.

3. Confirm that the horse is well. Check their temperature and report coughing, nasal discharge, appetite changes, colic or recent illness.

4. Discuss previous reactions. Mild soreness and anaphylaxis are very different problems and require different planning.

5. Complete the full catch-up course. Do not stop after the first injection if a second or third dose is required.

6. Record the next due date immediately. Include enough lead time for event rules, travel and seasonal disease risk.

Common Horse Vaccination Mistakes

Copying Another Horse’s Schedule

A neighbouring horse may have a different age, travel pattern, breeding status or medical history. Their schedule may also have been designed for another country.

Assuming Every Vaccine Is Annual

Some boosters are annual. Others may be recommended every six months, during specific months of pregnancy or only when a particular risk exists.

Waiting Until the Day Before an Event

Vaccination does not provide immediate protection. It may also cause temporary soreness or lethargy that interferes with travel or performance.

Treating Vaccination as an Outbreak Cure

Vaccination cannot replace isolation, testing, movement restrictions, temperature monitoring and disinfection. This is particularly important during EHV and strangles outbreaks.

Ignoring Product Storage and Administration

Vaccines can lose effectiveness if handled or stored incorrectly. Incorrect injection technique can also cause injury, abscessation or vaccine failure.

Forgetting Venue Requirements

A horse may be medically vaccinated but still be refused entry if the timing or documentation does not meet the venue’s rules.

Vaccination Is Only One Part of Disease Prevention

Vaccination reduces risk, but it does not create an invisible force field around the horse.

A strong prevention program should also include:

• Quarantining new arrivals

• Checking temperatures after travel or possible exposure

• Isolating horses with fever or respiratory signs

• Avoiding shared water buckets, tack and grooming equipment

• Cleaning trailers between horses

• Reducing standing water and mosquito breeding sites

• Maintaining accurate health and movement records

• Controlling human traffic during an outbreak

AAEP guidance emphasises that vaccination alone is not sufficient to prevent infectious disease transmission and that no vaccine should be expected to provide complete protection in every outbreak. (AAEP)

Frequently Asked Questions

Do horses need vaccinations every year?

Many vaccines require annual boosters, but not every horse needs every vaccine annually. Some high-risk horses require six-monthly boosters, while other vaccines are given only for specific geographical, breeding or exposure risks.

Should a pasture-only horse still be vaccinated?

Usually, yes. Pasture-only horses can still be exposed to tetanus, mosquitoes, wildlife and horses across fences. The actual vaccine list depends on the country and local disease risks.

Can several horse vaccines be given at the same appointment?

Often they can, but product compatibility, previous reactions, pregnancy and the horse’s health must be considered. Vaccines may be separated in horses with a history of reactions. The current Australian Hendra vaccine information also states that compatibility with other vaccines has not been established. (Zoetis)

Can a vaccinated horse still catch influenza, EHV or strangles?

Yes. Vaccination reduces the probability or severity of disease and may reduce shedding, but it does not guarantee complete protection. Biosecurity remains essential.

Can antibody titres be used instead of routine boosters?

For most equine vaccines, no validated protective antibody threshold has been established for routine field use. The AAEP does not currently recommend using antibody titres to decide whether most horse vaccine boosters are required. (AAEP)

Final Thoughts

If your horse is overdue, the answer is not to panic and it is not to wait another year. Review the records, assess the horse’s current exposure and arrange a catch-up plan with your veterinarian.

The most important correction is that there is no worldwide list of vaccines that every horse receives on exactly the same annual schedule. Core vaccines depend on geography, risk-based vaccines depend on lifestyle and several vaccines require carefully timed primary courses or six-monthly boosters.

A good vaccination plan protects the individual horse while also reducing the risk of disease spreading through stables, events and breeding properties.

ASK A VET™ can help you organise your horse’s vaccination records, track upcoming booster dates and seek veterinary guidance when you are unsure whether a missed dose, illness or previous reaction changes the plan.