In the United States, annual flu epidemics send more than 200,000 people to the hospital and kill as many as 49,000, according to the U.S. Centers for Disease Control and Prevention.
The leading cause of these hospitalizations and deaths is not flu itself, but pneumonia, which is a common complication of flu, according to Dr. Marc Siegel, an associate professor of medicine at NYU Langone Medical Center in New York City.