9 Core Horse Vaccines: What Each One Prevents, When to Give It, and Which Ones Your Horse Actually Needs
Most horse diseases don’t send a warning. Tetanus, rabies, and the mosquito-borne brain infections can go from “a bit off” to an emergency in days, and by then treatment options are limited. That’s why the core horse vaccines are the most useful habit in your yearly horse-care routine.
This guide walks through the 9 core horse vaccines, six core vaccines most horses receive, and three regional vaccines that depend on where you live and how your horse lives. For each one you’ll get what it prevents, when the first doses are due, how often to boost, and a practical tip you can use at your next vet visit.
What Are Core Horse Vaccines?
Core horse vaccines protect against diseases that are severe, easy to catch, or a risk to people, using vaccines with a strong safety record. Most horses should get them. The core vaccine for horses includes tetanus, encephalomyelitis, equine viral rhinopneumonitis, influenza, rabies and West Nile virus. It adds three regional vaccines.
Core vs. risk-based (regional) vaccines
Core vaccines are the baseline. They go into almost every horse’s plan.
Risk-based vaccines are added after your vet weighs your horse’s location, lifestyle, age, and exposure to other horses. Potomac horse fever, rotavirus, and strangles fall in regional vaccine group.
9 Core Horse Vaccines Overview
| Vaccine / disease | What it is | First doses and boosters |
|---|---|---|
| Core vaccines (6) | ||
| Tetanus | Bacterial infection that stiffens the muscles | Dose 1 at 6 months, then two more doses spaced 3–6 weeks apart. Booster every year. |
| Encephalomyelitis | Mosquito-borne viral infections that attack the nervous system | Same schedule as tetanus. |
| Equine viral rhinopneumonitis | Contagious viral infection of the respiratory tract | Same starting series as tetanus. Booster every 6 months. |
| Influenza | Contagious viral infection of the respiratory tract | Dose 1 at 6–9 months, dose 2 at 11 months. Booster every 6–12 months. |
| Rabies | Deadly viral disease | Dose 1 at 6 months, then doses at 7 months and at 1 year. Booster every year. |
| West Nile virus | Mosquito-borne viral infection | Dose 1 at 3–4 months, dose 2 one month later. Booster every 4–6 months. |
| Regional vaccines, important in certain areas (3) | ||
| Potomac horse fever | Bacterial disease that brings fever, low energy and diarrhea, and sometimes colic or laminitis (founder). Advised where the disease is common. | Dose 1 at 5–6 months, dose 2 four weeks later. Booster at 12 months, then every year. |
| Rotavirus | Viral diarrhea disease. Usually reserved for farms with a repeat problem. | Pregnant mares get a three-dose series before foaling. Foals are protected through colostrum, the first milk they nurse. |
| Strangles | Bacterial throat infection. Usually reserved for farms with a repeat problem. | Dose 1 at 4–6 months, then two more doses 4 weeks apart. Booster at 12 months, then every year. |
Boosters are where plans differ most. The chart below shows how often each vaccine comes around again.
Dark bar = shortest interval in the range. Light bar = upper end of the range. Rotavirus is not shown because it is given to pregnant mares (a three-dose series before foaling), not as a booster cycle.
Two things stand out. West Nile has the shortest booster cycle in MSD’s table. Tetanus, encephalomyelitis, and rabies are the “once a year” group that most owners can bundle into one spring visit.
First-Year Vaccination Timeline for Foals
A foal’s first year is the busiest vaccine year of its life. MSD’s schedule spreads the doses across the first 12 months, and several series overlap around 6 months of age. This timeline lines them up by age.
- 3–4 monthsWest Nile virus: dose 1
- 4–5 monthsWest Nile virus: dose 2, one month after dose 1
- 4–6 monthsStrangles (regional): dose 1. Doses 2 and 3 follow at 4-week intervals
- 5–6 monthsPotomac horse fever (regional): dose 1. Dose 2 follows 4 weeks later
- 6 monthsTetanus, encephalomyelitis, rhinopneumonitis and rabies: dose 1. The tetanus-style series (tetanus, encephalomyelitis, rhinopneumonitis) continues with two more doses, 3–6 weeks apart
- 6–9 monthsInfluenza: dose 1
- 7 monthsRabies: dose 2
- 11 monthsInfluenza: dose 2
- 12 monthsRabies: dose 3. Potomac horse fever and strangles boosters
Notice how much happens at 6 months. That’s one reason foals are often vaccinated in a single visit that covers several diseases through combination products. Ask your vet which combinations they use.
Why wait until about 6 months for most vaccines? Foals that nurse a vaccinated mare get antibodies through colostrum, the thick first milk. Foals are usually protected for up to 6 months.
Vaccinating too early can be less effective because those maternal antibodies can interfere. If the mare was unvaccinated or her history is unknown, your vet may start sooner.
The 6 Core Horse Vaccines Explained
1. Tetanus vaccine for horses
Quick answer: Tetanus is a bacterial infection that causes muscle tightening. MSD’s schedule gives the first dose at 6 months, two more doses 3–6 weeks apart, then a yearly booster.
Why it matters. Tetanus bacteria live in soil and manure, and their spores survive for a long time. They enter through wounds, including tiny punctures you’d never notice. Horses are very sensitive to the toxin the bacteria make, and it affects the nerves that control muscles.
Picture a horse that steps on a nail in a paddock: the wound closes over in a day, but the bacteria can keep multiplying beneath it.
Treating tetanus is difficult. Preventing it is simple.
Practical tip. If your horse has a deep wound or is going into surgery, and the last tetanus shot was more than six months ago, ask your vet about an extra booster.
Antibiotics for wound care, such as the ones covered in our guide to penicillin for horses, do not replace a tetanus booster.
2. Encephalomyelitis vaccine (Eastern and Western equine encephalitis)
Quick answer: Encephalomyelitis vaccines protect against mosquito-borne viruses that attack the nervous system. MSD uses the same schedule as tetanus: first dose at 6 months, two more 3–6 weeks apart, then a yearly booster.
Why it matters. These viruses cycle between birds and mosquitoes. Horses catch them from mosquito bites, and horses are not the main carriers, so a sick horse is not the usual source of infection for other horses.
The damage happens in the brain and spinal cord, which is why signs include fever, dullness, stumbling, and in severe cases collapse.
Eastern strain has a wide distribution, and that vaccines are available for Eastern, Western, and Venezuelan types. The AAEP lists Venezuelan encephalomyelitis as risk-based.
Practical tip. Time the shot for spring, before mosquito season. PetMD and CSU both suggest spring vaccination. PetMD adds that some vets shorten the interval to six months in high-risk regions. Many products combine encephalomyelitis with tetanus, and often West Nile too, so you may be covered in one injection.
3. Equine viral rhinopneumonitis vaccine (EHV-1 and EHV-4)
Quick answer: Rhinopneumonitis is a contagious viral respiratory infection. MSD uses the tetanus starting series, then boosts every 6 months.
Why it matters. The viruses behind it, equine herpesvirus 1 and 4, spread through nasal secretions, shared buckets, hands, and equipment. Many horses carry equine herpesviruses quietly for life and can shed them when stressed, so a healthy-looking horse can still pass it along at a show or boarding barn.
EHV-1 can also cause abortion in pregnant mares. Vaccination lowers the risk of respiratory disease and abortion, but no vaccine guarantees complete protection, so good biosecurity still matters.
Practical tip. Broodmares follow a pregnancy schedule. CSU gives doses at months 5, 7, and 9 of pregnancy (month 3 is optional) using a product labeled for abortion protection. CSU also suggests every 90 days for performance horses at higher risk. Note that AAEP classes this vaccine as risk-based, so ask your vet which level fits your horse.
4. Influenza vaccine for horses
Quick answer: Equine influenza is a contagious viral respiratory infection. MSD gives dose 1 at 6–9 months, dose 2 at 11 months, then a booster every 6–12 months.
Why it matters. Flu spreads fast wherever horses mix: shows, sales, trail rides, and boarding barns. Horses cough, run a fever, and have a nasal discharge, and recovery can drag on for weeks. MSD’s professional text recommends vaccinating every 6 months for horses exposed to other horses at events.
Flu viruses also change over time, which is one reason boosters keep coming. Some products are given into the nose rather than as an injection. CSU uses an intranasal vaccine for foals at 9 and 11 months.
Practical tip. If your horse travels, treat the 6-month end of MSD’s range as the safer plan, and schedule the second dose in the fall. PetMD lists influenza as annual for risk-based horses, so confirm with your vet.
5. Rabies vaccine for horses
Quick answer: Rabies is a deadly viral disease. MSD gives dose 1 at 6 months, further doses at 7 months and at 1 year, then a yearly booster.
Why it matters. Wild animals such as bats, skunks, raccoons, and foxes carry rabies, and it spreads through bites. Once signs appear it is essentially fatal. It is also a risk to people, which is a big reason it’s core on every major list. MSD’s professional text says all adult horses should be vaccinated every year.
Rabies can look like other problems, including colic, lameness, or other nerve diseases. If a horse shows sudden neurologic signs, call your vet right away and avoid contact with its saliva.
Practical tip. Keep the certificate. Boarding barns, shows, and some regions ask for proof. Note that CSU’s foal chart gives the first rabies dose at 7–8 months, while MSD starts at 6 months. Your vet will pick the timing based on the product and your area.
6. West Nile virus vaccine for horses
Quick answer: West Nile virus is a mosquito-borne viral infection. MSD gives dose 1 at 3–4 months, dose 2 one month later, then boosters every 4–6 months.
Why it matters. West Nile circulates between birds and mosquitoes, and horses are infected by bites. It attacks the nervous system, with signs that can include fever, weakness, muscle twitching, and stumbling, and some horses cannot stand.
Combination vaccines are available that include encephalomyelitis and West Nile together.
Practical tip: the booster interval question. MSD’s every 4–6 months interval is shorter than the annual spring schedule shown by PetMD and CSU. CSU adds that a fall booster can make sense when mosquitoes are heavy.
We can’t tell you which is right for your horse, because it depends on the specific vaccine and your local mosquito season. Ask your vet to pick one and write it in your horse’s record.
The 3 Regional Horse Vaccines
Regional vaccines are chosen for specific risks rather than given to every horse. They are the ones most worth discussing with your vet instead of assuming.
7. Potomac horse fever vaccine
Quick answer: Potomac horse fever is a bacterial disease that causes fever, low energy, and diarrhea, and sometimes colic or laminitis. Dose 1 at 5–6 months, dose 2 four weeks later, a booster at 12 months, then yearly.
Why it matters. The cause as Neorickettsia risticii. The disease is tied to certain waterside environments, so horses near creeks, rivers, or irrigated pastures are the ones vets worry about. Diarrhea can lead to dehydration, and laminitis (founder) is the complication owners fear most.
Practical tip. PetMD notes that vets may suggest boosters every 3–4 months for horses in endemic, high-risk areas. No vaccine is perfect, so ask your vet how well it performs where you live.
8. Rotavirus vaccine (for pregnant mares)
Quick answer: Rotavirus is a viral diarrheal disease of young foals. Vaccination is usually limited to farms with a recurring problem. Pregnant mares get a three-dose series before foaling, and the foal is protected through colostrum.
Why it matters. This vaccine is a hand-off. The mare is vaccinated, makes antibodies, and passes them to the foal in colostrum. That means the foal itself isn’t vaccinated, and it also means a foal that misses colostrum misses the protection.
Practical tip. CSU times the three doses at months 8, 9, and 10 of pregnancy. Foaling farms with past diarrhea outbreaks should raise this with their vet well before the due date.
9. Strangles vaccine for horses
Quick answer: Strangles is a bacterial infection of the throat. MSD says vaccination is usually restricted to farms with a recurring problem: dose 1 at 4–6 months, two more doses at 4-week intervals, a booster at 12 months, then yearly.
Why it matters. Strangles (caused by Streptococcus equi) is highly infectious. Horses run a fever, develop thick nasal discharge, and get swollen lymph nodes under the jaw that can burst. It spreads by direct contact and through shared buckets, tack, and hands.
Practical tip. CSU and PetMD both tie strangles vaccination to risk: horses that compete for much of the year or live at boarding and training barns are higher risk. Vaccination is one layer. Quarantine new arrivals and isolate any horse with a fever and nasal discharge.
Do you need the regional vaccines? A quick check
Why Vaccine Schedules Differ Between Sources
If you’ve compared your vet’s plan to a website, you’ve probably spotted differences. That’s normal. MSD, the AAEP, CSU, and PetMD each set categories and intervals a little differently. The table below puts them side by side so you can see exactly where.
| Vaccine | MSD category | AAEP category | Adult booster timing by source |
|---|---|---|---|
| Tetanus | Core | Core | MSD: every year. PetMD, CSU: annual. |
| Encephalomyelitis (EEE/WEE) | Core | Core | MSD: every year. PetMD, CSU: annual, in spring. PetMD: consider every 6 months in high-risk regions. |
| West Nile virus | Core | Core | MSD: every 4–6 months. PetMD, CSU: annual, in spring. CSU: fall booster if mosquitoes are heavy. |
| Rabies | Core | Core | MSD: every year. PetMD, CSU: annual. |
| Rhinopneumonitis (EHV-1, EHV-4) | Core | Risk-based | MSD: every 6 months. CSU: every 6 months for pleasure horses, every 90 days for at-risk performance horses. PetMD: annual. |
| Influenza | Core | Risk-based | MSD: every 6–12 months. CSU: every 6 months (spring and fall). PetMD: annual. |
| Potomac horse fever | Regional | Risk-based | MSD: every year. PetMD: every 6–12 months, or every 3–4 months in high-risk endemic areas. |
| Rotavirus | Regional | Risk-based | MSD: 3-dose series for pregnant mares. CSU: at months 8, 9 and 10 of pregnancy. |
| Strangles | Regional | Risk-based | MSD: every year after the 12-month booster. CSU, PetMD: every 6–12 months based on risk. |
Three differences matter most:
- West Nile boosters. MSD lists every 4–6 months; PetMD and CSU list annual spring vaccination.
- Rhinopneumonitis and influenza. MSD calls them core; AAEP calls them risk-based. Intervals range from every 90 days to annual depending on the horse’s risk.
- Rabies in foals. MSD starts at 6 months; CSU’s chart starts at 7–8 months.
When sources differ, your vet’s judgment, local disease reports, and the product label win. Those are the tiebreakers.
A Simple Yearly Vaccine Calendar
You don’t need to memorize intervals. You need a rhythm. This calendar groups the shots by season and situation.
Spring, before mosquito season
- Encephalomyelitis (EEE/WEE)
- West Nile virus
- Tetanus and rabies are often given at the same visit
- Influenza and rhinopneumonitis, first of two yearly rounds
Fall
- Influenza and rhinopneumonitis, second round
- West Nile booster if mosquitoes are heavy or your vet follows MSD’s 4–6 month interval
- Potomac horse fever booster if your area is high-risk
Before travel, shows or boarding
- Influenza: MSD advises every 6 months for horses at events
- Ask about strangles if you meet many new horses
- Check that tetanus is current if there is any wound risk
Broodmares
- Give boosters 4–6 weeks before foaling (CSU)
- Rhinopneumonitis at months 5, 7 and 9 of pregnancy, month 3 optional (CSU)
- Rotavirus three-dose series before foaling
- Use killed vaccines in pregnant mares (CSU)
Expert tip: book your spring and fall visits at the same time every year. A fixed month beats a mental note, and your vet’s office can send reminders.
Horse Vaccine Side Effects: What’s Normal and What Isn’t
Quick answer: Mild soreness, an occasional fever, and a quiet day or two are common after vaccination. MSD considers these normal. Hives, facial swelling, trouble breathing, or a growing hot swelling at the injection site need a vet.
Usually normal for 1–2 days (per MSD)
- Mild muscle soreness at the injection site
- An occasional low fever
- Acting quiet or eating a little less
Call your vet promptly
- Hives, or swelling of the face, lips or eyelids
- Labored breathing, sweating, trembling or collapse (emergency)
- A hot, painful, growing swelling at the injection site
- Fever, low appetite or stiffness lasting beyond 2 days
Check the injection site and your horse’s appetite the evening of the shot and again the next morning. If your horse runs a fever, ask your vet before giving anything. Some owners look up the correct amount for common anti-inflammatories such as Banamine dosage for horses or bute dosage for horses, but those are your vet’s call, especially right after a vaccine.
For mild hives, your vet may suggest an antihistamine. Our guides on Benadryl dosage for horses and cetirizine dosage for horses explain how those medications are typically dosed, but swelling around the face or any breathing difficulty is an emergency, not a home-treatment moment.
How to Prepare for Vaccine Day
A little prep makes the visit smoother and the plan better. Use this checklist.
- Bring your horse’s last vaccination records, or write down dates you remember.
- Tell your vet about travel, shows, boarding, breeding and new horses on the farm.
- Ask which combination vaccine (such as a 3-way or 5-way) fits your plan.
- Ask whether any regional vaccine makes sense for your farm this year.
- Check your horse’s temperature the morning of the visit. Skip vaccines if it’s elevated and ask your vet.
- Plan a light day afterward, with fresh water, hay and a short walk.
- Book the next booster before you leave the barn aisle, so it doesn’t slip.
Vaccines are one layer of horse health. Parasite control belongs in the same yearly conversation. If you’re building a wellness routine, our references on ivermectin dosage for horses and fenbendazole dosage for horses cover two of the most commonly used dewormers.
Frequently Asked Questions
What are the core vaccines for horses?
How many vaccines does a horse need?
How often should horses be vaccinated?
When should a foal get its first vaccines?
Is the rabies vaccine necessary for horses?
What is the 5-way vaccine for horses?
What is the best time of year to vaccinate a horse?
Can a vaccine make my horse sick?
Do indoor or retired horses still need vaccines?
Are strangles, Potomac horse fever and rotavirus vaccines necessary?
Do pregnant mares need different vaccines?
Why do the sources disagree on West Nile boosters?
Can I vaccinate my horse myself?
The Bottom Line: Build Your Plan Around Risk
The nine vaccines in MSD’s table give you a complete map: six core protections most horses need, plus three regional ones for specific situations. The biggest takeaways:
- Start most core series at about 6 months, with West Nile earlier at 3–4 months.
- Expect boosters every 4–6 months to once a year, depending on the vaccine.
- Treat regional vaccines as a risk conversation, not a default.
- When sources disagree, follow your vet and the vaccine label.
Your next step: pull out your horse’s vaccine record today. If you can’t find a date for tetanus, rabies, or West Nile, call your vet this week to fill the gaps and set your spring and fall visits.
Sources and Further Reading
- MSD Veterinary Manual: Core Vaccines Recommended for Horses
- MSD Veterinary Manual: Vaccinations for a Horse (pet owner version)
- MSD Veterinary Manual: Vaccination Program for Horses (professional version)
- American Association of Equine Practitioners: Vaccination Guidelines
- CSU Veterinary Health System: Equine vaccination guidelines
- PetMD: Horse Vaccines
