Seasonal influenza, commonly called the “flu,” is caused by the influenza virus, which infects the respiratory tract (nose, throat, lungs). Unlike many other viral respiratory infections, such as the common cold, the flu can cause a more severe illness and possibly life-threatening complications.
In the United States, flu season occurs in the fall and winter. The peak of flu season has occurred anywhere from late November through March. The overall health impact (e.g., infections, hospitalizations, and deaths) of a flu season varies from year to year. The U.S. Centers for Disease Control & Prevention (CDC) monitors circulating flu viruses and their related disease activity and provides influenza reports (called “ FluView”) each week from October through May. Flu surveillance in the U.S. continues through the summer months with condensed reports available.
Last reviewed March 2017