It happens every year. The days grow shorter, the temperature drops, footballs fly—and the flu strikes. Influenza, or the flu, is so common that it’s easy to dismiss this seasonal affliction as “just a virus” or “just the flu.” It’s true that the flu is caused by a virus and that most patients recover without specific therapy. But it’s also true that thousands of Americans die from the flu each year and millions are sick enough to miss work or school. Influenza is a serious infection —but it can be prevented and treated.