Novel A (H1N1) influenza is a new flu virus of swine origin that first caused illness in Mexico and the United States in March and April, 2009. It is thought that the H1N1 virus spreads in the same way that regular seasonal influenza viruses spread, through the coughs and sneezes of people who are sick with the virus, and by touching infected objects and then touching your nose or mouth.   H1N1 infection has been reported to cause a wide range of flu-like symptoms, including fever, cough, sore throat, body aches, headache, chills and fatigue.  The estimated incubation period could range from 1 to 7 days, although the incubation period for most cases will likely range from 1 to 4 days.   A summary of clinical features has been published by the WHO (Wkly Epi Rec 2009; 84:185-189).   Information on hospitalized cases in the US can be found at (MMWR 2009; 58(17):453-458 and MMWR 2009: 58(19): 536-541), while data concerning disease in pregnant woman due to the H1N1 virus is referenced at (MMWR 2009; 58(18)497-500).
 
With the H1N1 virus continuing to cause illness, hospitalizations, and deaths in the US during the normally flu-free summer months and some uncertainty about what the upcoming flu season might bring, the DoD along with the DHHS have taken important planning steps in preparation for an H1N1 vaccination effort to counter a possibly severe upcoming flu season.  Vaccines are the best tool we have to prevent influenza.