A “standard” vaccination program for all horses does not exist.  Each individual situation requires evaluation based on the following criteria: 

• Risk of infection (anticipated exposure, environmental factors, geographic factors, age, breed, use, and sex of the horse)

• Consequences of the disease (morbidity/mortality, zoonotic potential)

• Anticipated effectiveness of the selected product(s) 

• Potential for severe adverse reactions to a vaccine(s)

• Cost of immunization (time, labor, and vaccine costs) vs. potential cost of disease (time out of competition; impact of movement restrictions imposed in order to control an outbreak of contagious disease; cost of  treatment, or loss of life.)   

Note: The use of antibody titers or other immunological measurements to determine if booster vaccination is warranted is not currently recommended in the horse, as validated assays measuring protective levels of immunity have not been defined for most equine diseases.  A correlation between antibody levels and protective immunity under field conditions has not yet been established. Furthermore, equine vaccines are licensed based on efficacy data from experimental challenge studies, and may not correlate to antibody titers achieved in field conditions.

Clients should have realistic expectations and understand that: 

• Vaccination alone, in the absence of good management practices and biosecurity directed at infection prevention and control, is not sufficient to prevent infectious disease transmission. 

• Vaccination serves to minimize the risk of disease, but should not be expected to be fully preventative in all situations.

• A properly administered, licensed product should not be assumed to invariably provide complete protection during any given field outbreak.

• Protection is not immediately afforded to the patient after administration of a vaccine that is designed to induce active immunity. In most instances, a primary series of multiple vaccine doses must be administered initially for that vaccine to induce protective active immunity. 

• The primary series of vaccines and booster doses should be appropriately administered at least  14 days prior to likely exposure.

• Each horse in a population is neither protected to an equal degree nor for an equal duration following vaccination.

• All horses in a herd should be vaccinated at intervals based on manufacturer recommendations and the professional judgment of the attending veterinarian. 
  
  - Ideally, the same schedule is followed for all horses in a population, thus simplifying record keeping, minimizing replication and transmission of infectious agents in a herd and indirectly protecting those horses in the herd that responded poorly to vaccination, thereby optimizing herd-immunity. 

• Although rare, there is potential for adverse reactions despite appropriate handling and administration of vaccines.

Reviewed by the AAEP Infectious Disease Committee in 2021.