Most healthy people recover from the flu without problems, but certain people are at high risk for serious complications.

In the U.S., epidemiologists at the Centers for Disease Control (CDC)  work with states to collect, compile and analyze reports of flu outbreaks. More on the current situation.

Flu symptoms may include fever, coughing, sore throat, runny or stuffy nose, headaches, body aches, chills and fatigue. 

Annual outbreaks of the seasonal flu usually occur during the late fall through early spring. Most people have natural immunity, and a seasonal flu vaccine is available. In a typical year, approximately 5 to 20 percent of the population gets the seasonal flu. Flu-related deaths range from 3,300 to 48,600 (average 23,600).

A flu pandemic occurs when a new influenza A virus emerges for which there is little or no immunity in the human population; the virus causes serious illness and spreads easily from person-to-person worldwide. 

H5N1 (Bird) flu is an influenza A virus subtype that is highly contagious among birds. Rare human infections with the H5N1 (Bird) flu virus have occurred. The majority of confirmed cases have occurred in Asia, Africa, the Pacific, Europe and the Near East. Currently, the United States has no confirmed human H5N1 (Bird) flu infections, but H5N1 (Bird) flu remains a serious concern with the potential to cause a deadly pandemic.

For the 2009-2010 flu season, the H1N1 flu virus caused more illness in young people and pregnant women than is usual for prior flu seasons. Like seasonal flu, illness in people with H1N1 can vary from mild to severe.

Interactive Timeline on H1N1: The Year in Review
Follow the month-by-month development of the 2009 H1N1 flu pandemic.

2009 H1N1 Pandemic: Summary Highlights, April 2009-April 2010
Centers for Disease Control and Prevention document that summarizes key events of the 2009 H1N1 pandemic and CDC’s response activities.