As of the August 2010, H1N1 flu is no longer considered 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.
H1N1 flu is caused by a virus. It spreads from contact with an infected person. People with the flu can infect others through coughing and sneezing. Others can also get the flu by touching an infected object. People with certain health problems may have a higher risk of severe flu.
Symptoms of H1N1 flu may be:
A vaccine is a substance used to help protect people from certain infections. There are two types of H1N1 flu vaccine:
The H1N1 vaccine is advised for:
The Public Health Agency of Canada also includes:
The nasal spray will be given in 2 doses 1 month apart for children aged 2 to 9 years. People aged 10 to 49 years will only need 1 dose of the nasal spray vaccine.
The shot will be given in 2 doses 1 month apart to children aged 6 months to 9 years. Some doctors give the doses 3 weeks apart, instead of 1 month apart. People aged 10 years and older will only need 1 dose.
Any vaccine can cause serious problems. Examples are a severe allergic reaction. However, most people do not have any problems from the H1N1 vaccine. Some people have redness, warmth, or swelling near the injection site.
People who are allergic to eggs may want to avoid the H1N1 vaccine.
The nasal spray vaccine should not be given to:
Other ways to help prevent H1NI flu are:
During an outbreak, public health officials determine who is at risk. They issue guidelines and vaccinate people.
Centers for Disease Control and Prevention
European Commission—Health Information
European Medicines Agency
Public Health Agency of Canada
United Kingdom Department of Health
World Health Organization
Asthma information for patients and parents of patients. Centers for Disease Control and Prevention website. Available at: https://www.cdc.gov/H1N1flu/asthma.htm. Accessed April 7, 2021.
CDC advisors make recommendations for use of vaccine against novel H1N1, July 29, 2009. Centers for Disease Control website. Available at: https://www.cdc.gov/media/pressrel/2009/r090729b.htm. Accessed April 7, 2021.
Interim recommendations for facemask and respirator use to reduce novel influenza A (H1N1) virus transmission. Centers for Disease Control website. Available at: https://www.cdc.gov/h1n1flu/masks.htm. Accessed April 7, 2021.
Novel H1N1 flu (swine flu) and you. Centers for Disease Control website. Available at: https://www.cdc.gov/h1n1flu/qa.htm. April 7, 2021.
Novel H1N1 influenza vaccine. Centers for Disease Control website. Available at: https://www.cdc.gov/h1n1flu/vaccination/public/vaccination_qa_pub.htm. Accessed April 7, 2021.
US Food & Drug Administration. Influenza A (H1N1) 2009 monovalent vaccines questions and answers. US Food & Drug Administration website. Available at https://www.fda.gov/BiologicsBloodVaccines/Vaccines/QuestionsaboutVaccines/ucm182335.htm. Accessed April 7, 2021.
Last reviewed December 2020 by David L. Horn, MD, FACP
Last Updated: 4/7/2021