Model of influenza virus - Smithsonian Museum of Natural History - 2012-05-17
A model of the influenza virus, on display at the Smithsonian Museum of Natural History in Washington, D.C.
Influenza is a virus that causes chills, fever, aches and pains, severe headache, coughing, and fatigue. It lodges in the respiratory system; as the body runs a fever, becomes inflamed, and produces cells to fight the disease, the person feels ill. People die when these autoimmune responses overwhelm the body, causing too high a fever or too much phlegm in the lungs.
Tens of millions of people become infected with influenza every year, and between 250,000 and 500,000 people die from it. Flu kills 41,500 people in the U.S. every year.
Influenza mutates easily and quickly. There are many different forms of the virus, and some are more deadly then others. The 1918 flu probably killed 20 to 100 million people worldwide.