Vaccination against equine herpesvirus is one of those topics that deeply divides the horse community. While some consider it an essential part of stable health management, others are more hesitant – due to concerns about side effects, doubts about its effectiveness, or reports of possible neurological consequences. The debate around the herpes vaccine is often emotionally charged and sometimes shaped more by hearsay than by science. That’s exactly why it’s so important to take a closer look at the facts.
Regardless of personal opinion, horse owners should understand what equine herpesvirus actually is, what risks an infection can pose, how the vaccine works – and whether it’s truly worth it. Cost is certainly a factor, especially given the need for regular boosters, but at the core of the decision lies one key question: Is herpes vaccination a sensible step for protecting our horses – and for which ones does it make the most sense?
What is Equine Herpesvirus (EHV)?
Equine herpesvirus is a highly contagious disease affecting horses worldwide. The two most relevant types are:
EHV-1: causes respiratory illness, abortions in pregnant mares, and – most feared – the neurological form Equine Herpesvirus Myeloencephalopathy (EHM).
EHV-4: usually causes mild respiratory symptoms and rarely abortions.
Once infected, the virus remains latent in the horse’s body for life and can reactivate at any time, especially under stress. This is what makes herpes so tricky – even clinically healthy horses can shed the virus and infect others.
How dangerous is herpes infection?
While many horses show only mild symptoms like fever, nasal discharge, or coughing, the consequences can be severe:
Abortions in pregnant mares, particularly in late pregnancy
Rapid spread within stables, especially among young horses
Neurological symptoms like incoordination, hind limb weakness, or even recumbency
The neurological form (EHM) is rare but can have devastating outcomes. There is no cure – only supportive care. Some horses recover completely, while others may be permanently affected or need to be euthanized.
How does the herpes vaccine work?
The herpes vaccine is not a full protective shield but offers several important benefits:
Reduces virus shedding
Mitigates the severity of illness
Helps prevent abortions
Lowers infection pressure in the herd
Veterinary experts recommend it especially as a herd vaccination, as higher vaccination rates in a stable help protect even unvaccinated or vulnerable horses.
According to StIKo Vet (Germany’s Standing Veterinary Committee):
Initial series: two vaccinations 4–6 weeks apart
Booster shots every 6 months
Pregnant mares: specific vaccinations during the 5th, 7th, and 9th month of gestation
The controversy: Can the vaccine cause neurological issues?
A common concern is that the herpes vaccine could itself trigger neurological issues. However, there is no scientific evidence proving that vaccination causes EHM.
What can happen, though, is that stress or immune stimulation – including from a vaccine – might trigger a reactivation of a latent infection. In such cases, it’s not the vaccine causing the disease, but the already existing virus in the horse’s body being reactivated. This distinction is critical but often misunderstood.
Source: StIKo Vet – Friedrich-Loeffler-Institute: https://www.fli.de/en/topics/animal-health/animal-vaccines
Pros and Cons of Vaccination
Pros:
Prevents abortions
Reduces virus transmission
Minimizes outbreak risk in larger groups
Required for some competitions (e.g., German FN events)
Cons:
Requires regular boosters (every 6 months)
Not a full shield against EHM
Possible mild side effects (fever, fatigue, swelling at injection site)
Effectiveness can vary among individuals – personal risk assessment is key
Conclusion: A Decision Based on Balance and Knowledge
The herpes vaccine is not a miracle solution – but it’s often a useful tool in protecting horse health. Especially in larger barns, with pregnant mares or traveling horses, vaccination plays a valuable role. In smaller, closed horse groups, owners may decide on a case-by-case basis. One thing is certain: Vaccination alone is not enough – hygiene, monitoring and good stable management remain crucial.
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