Last winter, about 80,000 people in the United States died of flu and its complications, the Centers for Disease Control and Prevention said. This was the highest death toll in at least 40 years. Experts said it was such a deadly season because it was driven by the flu that typically sends more people to the hospital and particularly hits children and the elderly hard, and the vaccine did not work very well against that strain. The CDC said in recent years, between 12,000 and 56,000 people have died annually from the flu and its complications, including pneumonia, stroke, and heart attack.