The National Institutes of Health estimates that 5 to 20 percent of Americans come down with the seasonal flu each flu season.

Influenza (Flu)

According to the National Institute of Allergy and Infectious Diseases (NIAID), Influenza, or flu, is a respiratory infection caused by a variety of flu viruses. Flu viruses are classified as type A, B, or C. Type A viruses are found in many kinds of animals, including ducks, chickens, pigs, whales, and also in humans. The type B virus widely circulates in humans. Type C has been found in humans, pigs, and dogs and causes mild respiratory infections, but does not spark epidemics.

There are three main types of flu epidemics:

1. Seasonal Flu - This is the term used to refer to the flu outbreaks that occur yearly, mainly in the late fall and winter. It is estimated that between 5 and 20 percent of Americans come down with the flu every flu season.
2. Pandemic Flu - This term refers to particularly strong strains of flu that spread rapidly from person to person to create a world-wide epidemic (pandemic).
3. Avian Flu (Bird Flu) - In nature, the flu virus also occurs in wild aquatic and shore birds. It is possible for humans to contract bird flu, which has raised concerns that if this type of flu could at some point be transmitted between people, a new pandemic would occur.

There has also been an outbreak of H1N1 flu (swine flu), which originates from pigs.

Flu vaccines are generally given at the beginning of the "flu season," usually late October or early November in the U.S. People traveling to other countries should be aware that flu season may occur at different times in other parts of the world. You may wish to search for places to obtain a flu shot by entering a city and state or ZIP code.

Influenza vaccination by the Department of Veterans Affairs (VA) usually begins in September and October and continues through March or April each year. Veterans should check with their nearest VA medical facility to learn about local vaccination programs. You may also wish to view the VA's seasonal flu web page.

Flu.gov offers information about what you can do to prepare for the upcoming flu season and how to protect yourself against both H1N1 influenza and other types of flu. You may wish to access the H1N1 resource kit.

You may also wish to view answers to frequently asked questions about the flu.

For more information about the flu, please call the Centers for Disease Control and Prevention (CDC) at 1.800.CDC.INFO (1.800.232.4636).

December 5-11, 2010, is National Influenza Vaccination Week, a national observance that was established to highlight the importance of continuing influenza vaccination, as well as fostering greater use of flu vaccine after the holiday season into January and beyond.

Additional Resources:

• How to Tell the Difference between a Cold and the Flu
• Influenza (Flu) Information from the CDC
• Seasonal Flu Social Media Tools from CDC 
• Frequently Asked Questions about Flu Shots
• Flu Myths and Realities 
• Medicare Coverage of Flu Vaccines and Treatment
• State or Territorial Health Departments