Vaccine Strains Identified?

A study reported in the Journal of Veterinary Internal Medicine said it now is possible to differentiate between the "wild type" strain of S. equi and the modified live strain used in the intranasal vaccine Pinnacle IN. The research from the University of Minnesota on four post vaccinal "episodes" (three in Minnesota and one in Colorado) stated, "Results showed that all post vaccinal reaction strains from the four outbreaks and the intranasal vaccine strain were identical. Clear distinction was found between vaccine reaction strains/post vaccinal reaction strains, and the wild type strain.

"This finding clearly demonstrates that these horses exhibited complications as a result of vaccination. Whether these complications occurred from a return to virulence by the organism, immune reaction of the host, or inappropriate administration of the vaccine is unclear. Further work is necessary to understand the pathogenesis of this post vaccinal complication, which clearly has occurred as a result of the vaccine isolate."

Other researchers have not been able to distinguish the field strain of S. equi from the strain used in the Pinnacle IN vaccine using a similar approach. The unusual susceptibility of some horses to the vaccine strain of S. equi might be the cause of some of the reactions seen in vaccinated horses. This is much like some humans who become ill after receiving the flu vaccine, while others do not react.

About the Author

Kimberly S. Brown

Kimberly S. Brown was the Publisher/Editor of The Horse: Your Guide To Equine Health Care from June 2008 to March 2010, and she served in various positions at Blood-Horse Publications since 1980.

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