Influenza (Flu) Topic for comprehensive information on 2009 H1N1, seasonal, avian (bird), and pandemic flu.
Confirmed human cases of avian influenza A (H5N1)
Timeline of human and animal H5N1 infections since 1996 (PDF)
The genetic change that enables a flu strain to jump from one animal species to another, including humans, is called antigenic shift. Antigenic shift can happen in three ways:
The new strain may further evolve to spread from person to person. If so, a flu pandemic could arise.
Credit: This image is in the public domain. Please credit the National Institute of Allergy and Infectious Diseases (NIAID). Illustrator: Links Studio. Download: high resolution version of the Antigenic Shift illustration.
View Antigenic Drift
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Last Updated January 14, 2011