* Approximately 47% of the study cases had received at least one dose of the WNV vaccine before becoming infected; 3% were vaccinated after clinical signs of the disease were displayed; 50% were unvaccinated.
* The estimated case fatality rate for affected horses in Colorado and Nebraska was 28.6 percent.
* The fatality rate among WNV horses that had been vaccinated at least one time prior to onset of signs was 20.3%, while 36.6% of unvaccinated animals died or were euthanized.
* Only 13 WNV cases in the study were fully vaccinated based on current recommendations. Of these horses, the survival status of 12 is known and all 12 lived.
* Horses of all ages can apparently become infected with WNV.
* Of the surviving horses, 82% were considered fully recovered by their owners.

This article is written here with permission from Horse Illustrated, May 2003 issue.