NSAIDs Might Impair Horses' Response to Influenza Vaccines

Although vaccination against infectious disease is a routine component of horse care, many owners still voice concerns about their horse's risk of having an adverse reaction to these injections. For this reason, veterinarians sometimes administer non-steroidal anti-inflammatories (NSAIDs) before vaccinating horses to reduce the risk and severity of such reactions.

Researchers from the University of Kentucky (UK) recently hypothesized, however, that because NSAIDs inhibit COX inflammatory mediators, they might also inhibit horses' immune response to vaccination. Whitney Zoll, BS, a veterinary student at Michigan State University's College of Veterinary Medicine, teamed up with researchers from UK's Maxwell Gluck Equine Research Center to assess NSAIDs' effect on horses' response to a commercially available equine influenza vaccine. She presented the results of their study at the 2013 American Association of Equine Practitioners convention, held Dec. 7-11 in Nashville, Tenn.

"Although the reasoning behind the co-administration of an NSAID with vaccination may seem sound, such treatments could affect the ability of the horse to respond to the vaccine," Zoll explained.

In the first of the two-part study, she and colleagues employed 18 adult horses ages 2 to 5 that had been previously exposed to equine influenza. They administered the NSAID flunixin meglumine (commonly known as Banamine) to nine horses prior to vaccination, and the other nine animals served as controls, receiving only the vaccine.

In the second part of the study they employed 18 influenza-naive yearlings. They co-administered the vaccine and flunixin meglumine to six yearlings, administered only the vaccine to another six, and the remaining six animals served as unvaccinated controls.

Then, the researchers collected blood samples from all study horses before the initial vaccination as well as 7, 14, 21, and 28 days after vaccination and used two methods—enzyme-linked immunoassay (ELISA) and hemogglutination inhibition (HI)—to detect equine influenza-specific antibodies. They also used real-time PCR to measure cell-mediated immune (CMI) response to the vaccine.

From the adult horses, the team found that:

  • Vaccination increased the horses' influenza-specific HI antibodies and CMI response, though the IgG (immunoglobulin, or antibodies) response did not increase significantly;
  • NSAID treatment had no effect on the total IgG response to the vaccine;
  • NSAID administration significantly reduced the horses' HI antibody response to the vaccine; and
  • NSAID administration significantly reduced the horses' CMI response to the vaccine.

From the yearlings, the team found that:

  • At 28 days, vaccination resulted in an overall increase in IgG antibodies to equine influenza, as compared to the controls;
  • NSAID administration reduced the immunoglobulin Ga-specific response;
  • NSAID administration reduced, though not significantly, the HI antibody response; and
  • NSAID administration reduced the CMI response.

So what do all these results mean? "NSAID administration caused a significant decrease in immune response to influenza vaccine in both previously exposed and naive horses," Zoll concluded. "Thus, concurrent administration of NSAIDs when vaccinating can negatively impact a horse's immune response to the vaccine."

The study authors emphasized that veterinarians should take care when administering NSAIDs with vaccines, as they can reduce a vaccine's efficacy at stimulating antibody and CMI responses. As a result, horses with reduced immune responses might need to be vaccinated more frequently.

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More information on Gluck Equine Research Center and UK Ag Equine Programs.

Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.