Here's what the flu does to your body, and why it makes you feel so awful

National Broadcasting Company Influenza virus is an infection in your respiratory tract. Many of the symptoms are actually due to the body's immune response to the virus. To fight the infection in your lungs, your body releases cytokines into your bloodstream. As a result, they also affect other parts of the body, resulting in headaches, fatigue, and fever. Every year, from 5 to 20 percent of the people in the United States will become infected with influenza virus. Anaverage of 200,000of these ...