Seasonal Influenza (Flu)

Influenza (flu) is a contagious respiratory illness caused by influenza viruses. It infects the nose, throat, and sometimes the lungs. While flu viruses spread year-round, in the U.S., flu season begins in the fall and lasts through the following spring. The timing and length of flu seasons can vary, but cases of the flu influenza usually begin to increase in October and peak between December and February, with some flu cases occurring as late as May.