Equine Herpesvirus 1 Vaccine: Understanding the Basics

Equine herpesvirus 1 (EHV-1) is a highly contagious and often fatal disease affecting horses worldwide.

The virus has several strains, with EHV-1 being the most common and severe form.

EHV-1 can cause a range of symptoms, from mild respiratory issues to life-threatening neurological problems.

The vaccine is designed to protect horses against the most common strain of EHV-1, reducing the risk of severe symptoms and death.

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Inactivated vaccines are available for equine herpesvirus 1 (EHV-1), and they come in different forms, including those licensed for protection against respiratory disease and abortion.

Some inactivated respiratory vaccines perform better than others, with higher antibody responses and evidence of a cellular response to vaccination.

Modified live vaccines are also available, but they are only indicated for healthy horses 3 months of age or older as an aid in preventing respiratory disease caused by EHV-1.

Horses that have been naturally infected and recovered from EHV-1 are likely to have immunity that can last for 3 to 6 months, and booster vaccination can be resumed 6 months after the disease occurrence.

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Horses less than 5 years of age, horses on breeding farms, horses in contact with pregnant mares, and horses housed at facilities with frequent equine movement should be revaccinated at 6-month intervals.

Adult, non-breeding horses unvaccinated or having unknown vaccinal history should administer a primary series of 3 doses of inactivated EHV-1/EHV-4 vaccine or modified-live EHV-1 vaccine, with a 4- to 6-week interval between doses.

Here is a summary of vaccine recommendations for different groups of horses:

It's essential to note that vaccination is not a guarantee against EHV-1 infection, and strict quarantine, isolation, and monitoring protocols are more effective at controlling outbreaks than any vaccination protocol.

The vaccination schedule for EHV-1 varies depending on the horse's age and the type of vaccine used. Foals typically receive their initial vaccination at 5 to 6 months old.

Adult horses require booster vaccinations at least every six months to maintain some level of immunity. In pregnant mares, the only vaccine licensed to aid in the protection against EHV-1-induced abortion is to be used three times during pregnancy.

Inactivated vaccines are available, including those licensed for protection against both respiratory disease and abortion. Performance of these vaccines is superior, resulting in higher antibody responses and some evidence of a cellular response to vaccination.

Modified live vaccine is also available, indicated for the vaccination of healthy horses 3 months of age or older as an aid in preventing respiratory disease caused by EHV-1. However, none of the available vaccines have a label claim to prevent the neurologic form of EHV-1 infection.

Horses with a history of EHV infection and disease, including neurological disease, are likely to have immunity that can be expected to last for 3 to 6 months.

Here is a summary of the recommended vaccination schedules:

It's essential to note that vaccination is not a guarantee against EHV-1 infection, and good management practices, such as strict quarantine and isolation, are more effective at controlling outbreaks.

The early trials of EHV-1 vaccines were done with inactivated preparations after virus amplification in hamsters, but they caused severe local and systemic reactions.

These reactions were so severe that live virus preparations were introduced soon thereafter in controlled infection programs in mares.

The early- to mid-1960s saw the development of modified-live virus (MLV) vaccines, some of which are still in use today.

In the early 1960s, two main types of EHV-1 vaccines were developed: inactivated (killed) vaccines and MLVs.

Despite the development of MLV vaccines, the planned infection programs were only abandoned in the late 1970s due to the limited safety and efficacy of the vaccines.

The vaccines that were developed back in the 1960s have seen little to no changes in their production methods to this day.