Influenza, or "flu," is caused by a virus infecting the respiratory system, meaning your nose, throat, bronchial tubes, and lungs. Flu symptoms are usually more severe than those of the common cold and are more likely to affect other parts of your body. Flu also tends to come on suddenly while colds can develop gradually.

Flu is very contagious, spreading easily from one person to the next. Most people with healthy immune systems will get over the flu within 2 weeks, but young children, older adults, and people with chronic illnesses are more likely to develop complications such as pneumonia. About 35,000 people die of flu each year in the United States.

There are three types of flu viruses: A, B, and C. Type A viruses are the ones responsible for worldwide epidemics, such as the one in 1918 that killed as many as 50 million people worldwide. The avian or bird flu is a type A flu virus.

The best way to protect yourself from the flu is to get an annual vaccine (flu shot).

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Review Date: 9/29/2015  

Reviewed By: Steven D. Ehrlich, NMD, Solutions Acupuncture, a private practice specializing in complementary and alternative medicine, Phoenix, AZ. Review provided by VeriMed Healthcare Network. Also reviewed by the A.D.A.M. Editorial team.

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