Influenza, commonly known as the flu, is a contagious respiratory illness caused by influenza viruses. It can cause mild to severe illness and, in some cases, can lead to complications that can be life-threatening, especially in high-risk individuals. Also causes seasonal flu outbreaks but primarily affects humans and typically causes less severe illness than influenza A. Influenza spreads primarily through respiratory droplets when an infected person coughs, sneezes, or talks. It can also spread by touching surfaces or objects contaminated with the virus and then touching the face.
