“We were able to determine that she had the triggers in her bloodstream that would suggest that it comes from the vaccine,” said Dr. R. Todd Clark, assistant professor of emergency medicine at the University of Colorado School of Medicine. Dr. Clark knew the Centers for Disease Control and Prevention had warned against standard blood clot medicine to treat the side effect, but no alternative was clear. “We made the call for Bivalirudin based off of the best available evidence,” Dr. Clark said.