Potomac Horse Fever Vaccine

A recent article in The Chronicle of The Horse discussed the Potomac Horse Fever vaccine, starting with a story of a horse that despite being properly vaccinated, came down with the disease and required hospitalization (she fortunately did survive and is back to work). The efficacy of the vaccine has been the subject of debate for years. The horse from the article is not an uncommon story, and it is reasonable to ask if the vaccine is worth giving. In our opinion, the answer is “yes.” It’s important to not confuse correlation with causation, but in the experience in this practice over the last few decades, the number and severity of the PHF cases has dropped significantly. I think we benefit from the fact that vaccine development and testing was done with the strain from the Potomac River region, and get more effect from the vaccine than other parts of the country. We continue to recommend the AAEP guidelines, which is twice yearly vaccination in endemic areas.