Influenza (also called "the flu") is a viral infection in the nose, throat and lungs. About 10% to 20%. Some people can get very sick from the flu. Each year, about 200,000 people go to a hospital with the flu, and 36,000 people die because of the flu and complications. Flu viruses constantly change and mutate. Sometimes these mutations result in viruses that move from animals to humans because of antigenic shift. The new strain may evolve and spread rapidly from person to person. If so, it could result in a pandemic