Seasonal Flu Primer

Influenza (ihn-floo-ehn-zuh) (the flu) is a contagious respiratory illness caused by viruses that infect the nose, throat, and lungs. Exposure to these viruses can cause mild or severe illness and sometimes can lead to death. Flu season can begin as early as October and last as late as May. Seasonal flu activity usually peaks in January, February, or later.