It was a beautiful Saturday in the fall of 2005. The leaves in Cincinnati were changing colors, and Lisa Smith had just finished watching her son's soccer game.
She ran some errands, including something she'd been meaning to do for a week — get a flu shot. She stopped by her local pharmacy.
She didn't think about the shot again until a few days later, when she woke up feeling a bit strange. She had an odd tickle in her throat and her leg muscles were sore.
"Almost like I'd been exercising," she says.