by Scholten A

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.

What Is H1N1 Influenza?

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:

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

What Is the H1N1 Flu Vaccine?

A vaccine is a substance used to help protect people from certain infections. There are two types of H1N1 flu vaccine:

  • Shot given in the muscle
  • Nasal spray

Who Should Get Vaccinated and When?

The H1N1 vaccine is advised for:

  • Pregnant women
  • People who live with or care for a child under 6 months old
  • Healthcare workers and emergency medical staff
  • People aged 6 months to 24 years
  • People aged 25 to 64 years with long term health problems such as asthma or a weak immune system

The Public Health Agency of Canada also includes:

  • People living in remote areas
  • People handling pigs or poultry

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.

What Are the Risks Associated With the H1N1 Vaccine?

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.

Who Should Not Get Vaccinated?

People who are allergic to eggs may want to avoid the H1N1 vaccine.

The nasal spray vaccine should not be given to:

  • Those younger than 2 years or older than 50 years
  • Anyone with a severe, long term health problem or weak immune system
  • Pregnant women
  • Children under 18 years old—on long term aspirin therapy
  • Anyone who has had Guillan-Barre syndrome

What Other Ways Can H1N1 Be Prevented Besides Vaccination?

Other ways to help prevent H1NI flu are:

  • Washing hands often
  • Not touching the eyes, nose, and mouth
  • Avoiding close contact with sick people or their items, such as utensils
  • Wearing a disposable face mask

What Happens in the Event of an Outbreak?

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: 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: 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: Accessed April 7, 2021.

Novel H1N1 flu (swine flu) and you. Centers for Disease Control website. Available at: April 7, 2021.

Novel H1N1 influenza vaccine. Centers for Disease Control website. Available at: Accessed April 7, 2021.

US Food & Drug Administration. Influenza A (H1N1) 2009 monovalent vaccines questions and answers. US Food & Drug Administration website. Available at Accessed April 7, 2021.

Revision Information