Equine Vaccine Q&A

Can my horse be tested for antibodies to determine if vaccination is needed?

Recently, the idea of “checking titres” to determine if a horse needs to be vaccinated has become popular. Although this sounds straightforward, the correlation between protection and serological response to vaccination has not been well established for most equine vaccine antigens.

Serological testing to determine levels of circulating antibodies (titres) to specific pathogens may be used when potential adverse reactions pose greater risks than consequences from disease, or to assess potential non-responders (immunodeficient, diagnosed with pituitary parse intermedia dysfunction, etc.).

However, it is important to remember that circulating antibodies are only part of the immune response. Immune responses can occur throughout the body, as evidenced by pathogen-specific 

antibodies in the blood, or locally in which antibodies may remain in particular areas of the body and not be present in the bloodstream. As such, there are limitations to evaluating titres 

with respect to specific pathogens. The correlation depends on the specific disease, the route of vaccine administration, the type of vaccine, and the strength of the immune response. 

Is it OK to change vaccine manufacturers?

It is unlikely that horses will receive the same vaccine products regularly throughout their lives for many reasons (change of ownership, location, vaccine shortage, etc.). Products from different manufacturers are regularly used interchangeably. To date, research of impacts on immune response and subsequent protection is sparse.

The number of possible vaccine combinations is large, so it is difficult to provide conclusions for particular products. The answer essentially depends on how different or similar vaccines are to one another. In some cases, utilizing different products may induce a superior immune response. However, there are many factors to take into consideration, such as the age of the horse and time since last immunization.

UC Davis researchers reported results of a Center for Equine Health supported study that investigated immune response to equine influenza virus vaccines from different manufacturers in previously immunized, healthy, adult horses. The data showed similar antibody responses across groups, even after a booster, suggesting the specific equine influenza vaccine manufacturer should not be a primary concern.