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H1N1 influenza (Swine flu)


The H1N1 virus (swine flu) is an infection of the nose, throat, and lungs. It is caused by the H1N1 influenza virus.

Alternative Names

Swine flu; H1N1 type A influenza


Earlier forms of the H1N1 virus were found in pigs (swine). Over time, the virus changed (mutated) and infected humans. H1N1 is a new virus first detected in humans in 2009. It spread quickly around the world.

The H1N1 virus is one of the three viruses included in the regular (seasonal) flu vaccine.

You cannot get H1N1 flu virus from eating pork or any other food, drinking water, swimming in pools, or using hot tubs or saunas.

Any flu virus can spread from person to person when:

  • Someone with the flu coughs or sneezes into air that others breathe in.
  • Someone touches a doorknob, desk, computer, or counter with the flu virus on it and then touches their mouth, eyes, or nose.
  • Someone touches mucus while taking care of a child or adult who is ill with the flu.


Strikas RA; Centers for Disease Control and Prevention (CDC); Advisory Committee on Immunization Practices (ACIP); ACIP Child/Adolescent Immunization Work Group. Advisory committee on immunization practices recommended immunization schedules for persons aged 0 through 18 years--United States, 2015. MMWR Morb Mortal Wkly Rep. 2015;64:93-94. PMID: 25654610

Treanor JJ. Influenza (including avian influenza and swine influenza). In: Bennett JE, Dolin R, Blaser MJ, eds. Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases. 8th ed. Philadelphia, PA: Elsevier Saunders; 2015:chap 167.

Review Date: 5/3/2015
Reviewed By: Laura J. Martin, MD, MPH, ABIM Board Certified in Internal Medicine and Hospice and Palliative Medicine, Atlanta, GA. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.
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