Anthrax is a serious septicemic disease caused by proliferation and spread of the vegetative form of Bacillus anthracis in the body. Infection is acquired though ingestion, inhalation or contamination of wounds, or mechanical transmission by blood sucking insects of spores of the organism. Anthrax is encountered only in limited geographic areas where alkaline soil conditions favor survival of the spores. Anthrax has a high mortality rate and zoonotic potential. Vaccination is indicated only for horses pastured in endemic areas.


The only vaccine currently licensed for use in horses is a live acapsular Sterne strain, spore-form. The vaccine has been shown to be effective; however, vaccination of pregnant mares is not recommended. Adverse reactions to the vaccine have been reported in young, and miniature horses. Local swelling may occur at the injection site, most of which resolves within a few days.

Appropriate caution should be used during storage, handling and administration of this live bacterial product. Consult a physician immediately if human exposure to the vaccine occurs through accidental injection, ingestion, or otherwise through the conjunctiva or broken skin.

Antimicrobial drugs should not be given concurrently, as this may interfere with adequate response to the vaccine.

Vaccination Schedule:

  • Adult horses (previously vaccinated, unvaccinated, and unknown vaccination history) against anthrax:  Annual vaccination. Vaccinate 4 weeks prior to turnout on pastures in endemic areas.  A second dose may be used 2-3 weeks after first dose in heavily contaminated environments.
  • Pregnant mares: Not recommended.
  • Foals: There is no specific information available regarding the vaccination of foals against anthrax.
  • Outbreak: Vaccinate afebrile horses not showing clinical signs.

Reviewed and revised 2019

Resource Type

  • Guideline


  • Vaccinations

Publish Date

April 19, 2024