A contagious respiratory illness caused by influenza viruses. It can cause mild to severe illness and in some cases, can lead to death. The best way to prevent seasonal flu is getting a flu vaccination each year (CDC, 2009).
H1N1 (also referred to as “swine flu”) is a new influenza virus causing illness in people. This new virus was first detected in people in the United States in April 2009. Other countries, including Mexico and Canada, have reported cases of this illness. This virus is transmitted person-to-person, in much the same way that regular seasonal influenza viruses spread (CDC, 2009).
From flu.gov
World Health Organization H1N1 Global Information
The Center for Disease Control and Prevention - H1N1 information (Spanish)