The H1N1 virus (swine flu) was a new flu virus strain that caused a worldwide pandemic in humans from June 2009 to August 2010.
The Centers for Disease Control and Prevention now call the virus 2009 H1N1.
Earlier forms of the H1N1 virus were found in pigs. Over time, the virus changed (mutated) and infected humans. H1N1 was a new virus in humans in 2009, and it spread quickly around the world. Most of the people who got the H1N1 flu were ages 5 - 24.
During the 2010-2011 flu season, H1N1 virus (swine flu) did not cause widespread infections as it had in 2009-2010. The 2010-2011 seasonal flu vaccine also protected against swine flu, and a separate vaccine was not needed. The same is true for the 2011-2012 seasonal flu vaccine
Any flu virus can spread from person to person when:
You cannot get H1N1 flu virus from eating pork or any other food, drinking water, swimming in pools, or using hot tubs or saunas.
See also: Influenza vaccine.
Centers for Disease Control and Prevention (CDC). Prevention and Control of Influenza with Vaccines: Recommendations of the Advisory Committee on Immunization Practices (ACIP), 2011. MMWR. 2011 Aug 26;60:1128-32.