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H1N1 Influenza

  • Amy Scholten, MPH
Publication Type:


H1N1 Influenza

(Swine Flu; Swine Influenza; Human Swine Flu; Global Swine Flu; Pig Flu; Novel H1N1 Flu; New H1N1 Flu; H1N1 Flu; H1N1 Infection; Influenza A (H1N1); Type A (H1N1) Flu)

As of August 2010, H1N1 flu is no longer a pandemic. This fact sheet provides historical information about H1N1 flu. It will no longer be updated.


H1N1 flu is a respiratory infection. It can cause mild to severe illness.


The H1N1 flu is caused by a virus. It spreads by:

  • Breathing in droplets—after an infected person coughs or sneezes
  • Touching a contaminated surface—and then touching the eyes, nose, or mouth
Pandemic H1N1 Virus. H1N1 virus

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Risk Factors

The H1N1 flu is more common in people under 25 years old. The main risk for H1N1 flu is contact with a person who has it.

The risk for severe H1N1 infection is higher with:

  • People in certain age groups, such as those:
    • Younger than 2 years old
    • 65 years or older
  • Long-term aspirin use— in those younger than age 19
  • Pregnancy or recent birth
  • Diabetes
  • A weak immune system
  • Long term lung, heart, kidney, liver, nerve, or blood problems
  • Living in a long term care facility
  • Obesity


Symptoms of H1N1 flu may range from mild to severe. They may be:

  • Fever and chills
  • Sore throat
  • Cough
  • Severe muscle aches
  • Being very tired
  • Headache
  • Runny or stuffy nose
  • Nausea, diarrhea, or vomiting

If H1N1 flu becomes severe, it can cause pneumonia.


The doctor will ask about your symptoms and health history. Diagnosis may be based on symptoms.

A nose or throat swab may be taken and tested. This can confirm the diagnosis.


The goal is to ease symptoms and prevent problems. Those with severe illness may need hospital care.

Treatment options may be:

  • Rest and fluids
  • Over-the-counter pain medicine
  • Medicines to ease cough or stuffy nose
  • Saline nasal sprays
  • Certain antiviral medicines—for those with severe illness or who are at risk for it


The risk of H1N1 flu may be reduced by:

  • Taking the H1N1 flu vaccine
  • Taking certain antiviral medicines—for people with a high risk
  • Washing hands frequently
  • Not touching the eyes, nose, and mouth
  • Avoiding close contact with sick people or their items, such as utensils




  • 2009 H1N1 flu. Centers for Disease Control and Prevention website. Available at: https://www.cdc.gov/h1n1flu. Accessed April 7, 2021.
  • Influenza in adults. EBSCO DynaMed website. Available at: https://www.dynamed.com/condition/influenza-in-adults. Accessed April 7, 2021.
  • Lee RU, Phillips CJ, et al. Seasonal influenza vaccine impact on pandemic H1N1 vaccine efficacy. Clin Infect Dis. 2019;68(11):1839-1846.
  • Seasonal influenza: flu basics. Centers for Disease Control and Prevention website. Available at: https://www.cdc.gov/flu/about/index.html. Accessed April 7, 2021.
  • Traveler's health. Centers for Disease Control and Prevention. Available at: https://wwwnc.cdc.gov/travel. Accessed April 7, 2021.


  • David L. Horn, MD, FACP
Last Updated:

This content is reviewed regularly and is updated when new and relevant evidence is made available. This information is neither intended nor implied to be a substitute for professional medical advice. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with questions regarding a medical condition.