Vaccination Recommendations




Performance Horses

Pleasure Horses



(EHV-1 and EHV-4)

First dose: 4 to 6 m.
Second dose: 5 to 7 m.
Third dose: 6 to 8 m.
Then at 3-m. intervals

Booster every 3 to 4 months up to annually

Booster every 3 to 4 months up to annually Optional: semiannual if elected
Fifth, seventh, ninth month of gestation (inactivated EHV-1 vaccine); optional dose at third month of gestation

Vaccination of mares before breeding and 4 to 6 weeks prepartum is suggested. Breeding stallions should be vaccinated before the breeding season and semiannually

Table adapted from

Why should I vaccinate against EHV?
While vaccinating for EHV-1 and EHV-4 does not prevent horses from becoming infected with EHV and it does not prevent horses from becoming clinically ill, it may lessen the severity and duration of clinical signs and decrease viral shedding (9).  This will not only improve the prognosis for your horse but also decrease the risk of other horses contracting the infection.  Vaccinated horses are thought to have a reduced incidence of viremia resulting in a reduced chance of sequelae such as abortion or encephalomyelopathy.  Vaccination induces a short lived immunity and thus frequent vaccinations are recommended to maximize protection against EHV-1 and EHV-4.  See the table above for the vaccination protocol recommended by the AAEP (10).  Vaccinating against EHV has been controversial as some individuals felt that this may render the horse more susceptible to developing the neurological form of the disease.  However, to date there have been no reported incidences of the modified live vaccine for EHV-1 causing neurological disease (20).

Current Vaccines:
Current vaccines available commercially in North America include inactivated vaccines for EHV-1, EHV-4; the vaccines may include one or all of these serotypes in them, depending on the company that you purchase the vaccine from (21).  Inactivated vaccines consist of killed virus and while they typically produce fewer side effects than modified live vaccines, they are also usually more expensive and the protection may be shorter lived.  Modified live vaccines against EHV-1 are available commercially and these consist of live EHV-1 virus that has been modified such that it elicits a cell mediated and humoral immune response without causing disease in the horse.  No vaccines are protective against encephalomyelopathies due to EHV.<>