Flu is a disease of the body’s breathing system, including the nose, throat and lungs. Flu is short for “influenza.” Flu is caused by a virus. In New England, the yearly flu season usually begins in the fall and lasts through March. Flu that occurs every winter season is called “seasonal flu.” New and very different flu viruses that appear every 30-40 years, like the H1N1 flu virus in 2009, are called “pandemic flu.” Seasonal flu and pandemic flu have similar symptoms, are spread the same way, and are prevented the same way.
Massachusetts Department of Public Health website on influenza
Center for Disease Control (CDC) websites on flu