Equine Herpesvirus Vaccination by a Vet – 2025 Guide to Reducing Neurologic Risk 💉🐴

By Dr Duncan Houston, BVSc

Introduction

Equine herpesvirus-1 (EHV-1) is known for causing respiratory disease, abortion in pregnant mares, and in some cases, a devastating neurological form known as Equine Herpes Myeloencephalopathy (EHM). While vaccines exist, none are currently licensed to prevent the neurologic strain. In this 2025 vet-reviewed guide, we examine what vaccination can do, what it can’t, and what recent research reveals about using high-antigen vaccines to reduce disease severity.

What Is Equine Herpesvirus (EHV)? 🦠

• Caused by equine herpesvirus-1 (EHV-1) and equine herpesvirus-4 (EHV-4)
• EHV-1 causes:
  • Respiratory disease
  • Abortion in pregnant mares
  • Neurological form (EHM)
• Latent virus—can lie dormant for years and reactivate under stress
• Spreads through respiratory secretions and contaminated equipment

Vaccines: What They Can and Can’t Do 💉

• Licensed to protect against: Respiratory disease and abortion
• Not licensed to prevent: Neurologic form (EHM)
• Vaccinated horses can still get EHM—but severity may be reduced

Concerns About Neurologic Risk Post-Vaccination 😟

• Some reports suggest vaccinated horses have developed neurologic disease
• Hypothesis: immune response might intensify inflammation in CNS in rare cases
• But evidence remains inconclusive—risk appears extremely low

Oklahoma State Study: What We Know 🧪

To better understand vaccine effectiveness against neurologic EHV:

• Study setup: 6 aged mares vaccinated 3 times with Pneumabort-K (high-antigen vaccine), and 6 unvaccinated controls
• Exposure: All 12 horses were exposed to a neurologic EHV-1 strain
• Results:
  • 5 of 6 unvaccinated mares developed severe neurologic signs
  • Only 1 of 6 vaccinated mares showed severe signs
  • Vaccinated horses had milder clinical signs overall

What This Means in 2025 🧬

• Vaccination with high-antigen vaccines may reduce the severity of EHM
• No vaccine prevents the disease entirely—outbreak biosecurity is still essential
• Boosting horses before high-risk events (e.g., large shows) is advised

Recommended Vaccination Protocols 📋

Performance Horses:

• Vaccinate every 6 months with high-antigen EHV-1/4 vaccine
• Boost 3–4 weeks before high-risk exposure

Pregnant Mares:

• Vaccinate at 5, 7, and 9 months of gestation using labeled inactivated vaccine (e.g., Pneumabort-K)

Young Horses:

• Start series at 4–6 months old
• Follow with boosters per vet schedule

Choosing a Vaccine 🧾

• Pneumabort-K: High-antigen vaccine used in study—recommended for pregnant mares
• Rhinomune®, Calvenza®, or Prestige® EHV: Discuss options with your vet to match your herd’s exposure risk

Outbreak Response Protocols 🛑

• Isolate all horses with fever or neurologic signs
• Monitor rectal temperatures twice daily
• Stop horse movement on/off premises for 21+ days
• Disinfect all shared gear, stalls, and trailers

When Not to Vaccinate ❌

• During or shortly after exposure
• Horses with current symptoms or recent fever
• In stressed or ill horses without vet supervision

Case Example: Show Barn Booster Success

1. A show barn vaccinates with high-antigen EHV booster 30 days before a national event
2. Despite exposure at the event, only one horse develops mild fever
3. All horses are monitored post-show—no neurological signs appear

FAQs

Q: Should I vaccinate if my horse is exposed?

A: No—wait until the outbreak is over. Vaccination during exposure may not prevent disease and could complicate diagnosis.

Q: Can vaccines cause EHM?

A: There is no proven causal link. The neurologic form can affect vaccinated or unvaccinated horses.

Q: Are booster shots really necessary?

A: Yes—for high-risk horses, boosters help reduce viral shedding and disease severity.

Conclusion

Vaccination remains a powerful tool against equine herpesvirus, especially the respiratory and abortion strains. While current vaccines aren’t labeled to prevent the neurologic form, high-antigen options appear to reduce severity and spread. In 2025, talk to your vet about the best vaccine strategy for your horse—especially before travel, breeding, or competition season.

Need help building a vaccination plan? Visit AskAVet.com or use our app 📱 to consult Dr Duncan Houston and the veterinary team for custom recommendations. 🩺🐴