Flu refers to illnesses caused by a number of different influenza viruses. Flu can cause a range of symptoms and effects, from mild to lethal.

Two strains of flu, seasonal flu and the H1N1 (Swine) flu, are currently circulating in the United States. On June 9, 2009 the World Health Organization (WHO) declared that a global pandemic of H1N1 (Swine) flu is underway, and on October 24, 2009, U.S. President Obama declared the 2009 H1N1 influenza pandemic a National Emergency.

Annual outbreaks of the seasonal flu usually occur during the late fall through early spring. Most people have some 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 and approximately 36,000 flu-related deaths are reported.

This year, the H1N1 (Swine) flu virus may cause a more dangerous flu season with a lot more people getting sick, being hospitalized and dying than during a regular flu season. H1N1 (Swine Flu) is a new virus first seen in the United States. It is contagious and spreads from person to person. Like seasonal flu, illness in people with H1N1 can vary from mild to severe.

Source: www.flu.gov