2009 H1N1 flu (sometimes called “swine flu”) is a new influenza virus that is spreading worldwide. Because this virus is very different from current seasonal influenza viruses, many people will not have protective immunity against it, and the seasonal flu vaccine will not protect against it.

Influenza is unpredictable, but this flu season could be worse than recent years because of the 2009 H1N1 virus. CDC is preparing for an early flu season and expects both 2009 H1N1 flu and seasonal flu to cause illness, hospital stays and deaths this season. Click here for more up-to-date information.