Influenza is an infection of the nose, throat, and lungs caused by the influenza virus. Symptoms include fatigue, fever, headache, dry cough, sore throat, runny nose, and sore muscles. Some people have stomach problems or diarrhea. The flu is thought to spread mainly from person to person through coughing and sneezing of infected people.

Pandemic influenza is a global outbreak of a new influenza A virus that causes serious illness. People have little or no immunity to the virus, and the disease easily spreads from person to person worldwide in a very short time.

Learn what to do if you have the flu.