WNV Vaccine: Safe for Broodmares

Researchers at Texas A&M University (TAMU) have just completed a retrospective study into the safety of administering the killed West Nile virus (WNV) vaccine to pregnant broodmares, the first study on this topic in equine reproductive research. The study looked at 595 mares from four different farms in Texas and Kentucky. The authors of the study (which was published in the Journal of the American Veterinary Medical Association) hoped to resolve the dispute of whether administration of the vaccine caused reproductive losses in pregnant broodmares.

"The main reason we did the study was to investigate the validity of anecdotal claims made by lay journals and web sites concerning infertility, pregnancy loss, and fetal abnormalities associated with administration of this vaccine to pregnant mares," said Joey Vest, DVM, lead author of the study and equine theriogenology resident at TAMU.

"Given the widespread concerns expressed and possible adverse outcomes of vaccinating pregnant mares, we felt it would be important to systematically evaluate whether there was any association of administration of the killed WNV vaccine and adverse outcomes during pregnancy," said Noah Cohen, DVM, PhD, Dipl. ACVIM, the author responsible for statistical and epidemiological data analysis.

Terry L. Blanchard, DVM, MS, Dipl. ACT, one of the study's authors and TAMU professor of theriogenology, said, "We felt it was important to get the best safety information we could. After reviewing our results, we feel comfortable using the vaccine in pregnant mares, but you must realize this study was not a vaccine safety trial, as such."

The authors reviewed the mares' medical histories to include vaccination date(s) and whether a pregnancy loss occurred. According to the study, "The overall incidence of pregnancy loss in (vaccinated) mares fell within the normal range of typical losses and mares vaccinated during any period of pregnancy were not any more likely than mares not vaccinated during that same period of pregnancy to lose their foals," said Vest.

Researchers hope this study gives vets more of a comfort zone when deciding to vaccinate mares. "This study should alleviate some of the horse owners' fears that there are any adverse reproductive side effects to the WNV vaccine," said Blanchard.

About the Author

John V. Wood

John V. Wood is an Emmy Award-winning journalist, and now teaches his craft to high school students in North Carolina. Wood has been published in numerous national magazines/newspapersover his career, and published his first book in June 2010. Wood currently lives in Willow Spring, NC.

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