What Causes the Flu?
How Long Am I Contagious After I Get the Flu?
You are contagious for up to seven days after the onset of the flu, although the flu virus can be detected in secretions up to 24 hours before the onset of symptoms. This means you might transmit the flu virus a full day before your flu symptoms begin.
In young children, the flu virus can still be spread in the secretions even into the second week of illness.
How Can I Prevent the Flu?
To prevent the flu, be sure to keep your hands clean -- wash them frequently to remove germs -- and get a flu shot. The CDC develops a flu vaccine based on the type A strain that they believe will be most prevalent in the coming flu season. This is the vaccine you get with the annual flu shot or FluMist nasal spray.
For in-depth information, see WebMD's Flu Shot: Influenza Vaccine.
Also, see WebMD's What Is FluMist?