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Pandemic (H1N1) Influenza Vaccine

As of the August 2010 pandemic, H1N1 flu is no longer considered a pandemic. This fact sheet provides historical information about pandemic H1N1 flu and will no longer be updated. Please see the Centers for Disease Control and Prevention website at http://www.cdc.gov/h1n1flu for the latest information about H1N1 flu.

What Is Pandemic (H1N1) Influenza?

Pandemic H1N1 flu (originally called swine flu) is a respiratory infection. The pandemic H1N1 flu has spread to humans and has reached the level of a pandemic. A pandemic is a worldwide outbreak.

The main risk factor for getting the pandemic H1N1 flu is contact with an infected person. People with the flu can infect others through coughing and sneezing. You can also get the flu by touching an infected object. A chronic health condition such as heart or lung disease, diabetes, or cancer may increase your risk of a more severe form of the flu.

Symptoms may include:

  • Fever and chills
  • Sore throat
  • Cough
  • Severe muscle aches
  • Severe fatigue
  • Headache
  • Runny nose, nasal congestion
  • Sneezing
  • Watery eyes
  • Stomach symptoms like nausea, vomiting, and diarrhea

Most people recover at home. Basic care includes rest, fluids, and over the counter pain relievers. Antiviral medications may be used. They may be given to prevent or treat an H1N1 infection.

What Is the H1N1 Flu Vaccine?

A vaccine is a substance used to protect people from infections caused by bacteria and viruses. There are 2 ways you might receive the H1N1 flu vaccine:

  • Shot given in the muscle—uses inactivated vaccine containing dead virus
  • Nasal spray—uses live, attenuated vaccine containing weakened virus

The virus in a vaccine will not make you sick. Be aware that even if you have been vaccinated, you can still get the pandemic H1N1 flu. If you have symptoms, tell your doctor.

Is the H1N1 Flu Vaccine Available?

Yes, the H1N1 flu vaccine is available. The supply varies by location.

Who Should Get Vaccinated and When?

According to the Centers for Disease Control and Prevention (CDC), those who should get vaccinated include:

  • Pregnant women
  • Anyone who lives with or cares for a child under the age of 6 months
  • Healthcare workers and emergency medical personnel
  • People aged 6 months to 24 years
  • People aged 25 to 64 years with chronic medical conditions such as asthma or compromised immune systems

The Public Health Agency of Canada has similar target groups to the CDC, but also include:

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

People in these target groups who have had flu-like illness not confirmed to be pandemic H1N1 flu should still be vaccinated.

Pregnant women should be given the flu shot (the inactivated vaccine), not the nasal spray (live, attenuated vaccine).

Should there be a shortage of vaccine, the target populations would consist of:

  • Pregnant women
  • Anyone who lives with or cares for a child under the age of 6 months
  • Healthcare workers and emergency medical personnel
  • People aged 6 months to 4 years
  • Children aged 5 to 18 years with chronic medical conditions

After the target groups, people aged 25 to 64 years should get the vaccine. Older adults (over 65 years) will be the last group to receive the vaccine. Older adults have been less likely to become infected with this flu than younger people.

The nasal spray will be given in 2 doses 1 month apart for children aged 2 to 9 years. Talk to your child's doctor about what is best for your child. 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 say it is fine to give the doses 3 weeks apart, instead of 1 month apart. Talk to your child's doctor about what is best for your child. People aged 10 years and older will only need 1 dose.

Flu season can begin as early as October and last as late as April or May. The best time to get vaccinated is as soon as the vaccine becomes available. Doing so will protect you before the flu comes to your community. The flu season can extend into the spring, so it is important to still get vaccinated if you did not do so early in the season.

Make sure you talk to your healthcare provider about which vaccine is right for you.

Who Should Not Get Vaccinated?

At this time, you may not want to get the vaccine if you are allergic to eggs. This is because most vaccines will be made using eggs. Further testing on the H1N1 flu vaccine may indicate that other people need to be cautious as well. Talk to your doctor to learn more.

The nasal spray (live, attenuated vaccine) should not be given to:

  • Those younger than 2 years or older than 50 years
  • Anyone with a severe chronic medical condition or weakened immune system
  • Pregnant women
  • Children under 18 years old taking chronic aspirin therapy

Is the H1N1 Flu Vaccine Safe?

Like the seasonal flu vaccine, the H1N1 flu vaccine is not expected to cause problems other than soreness at the injection site. People with specific allergies (eggs, latex, or certain drugs) should check with their doctor before receiving any flu vaccine.

In 1976, a flu vaccine was linked with cases of Guillan-Barre syndrome (GBS), a rare nerve disease causing weakness for several weeks, with some cases being severe enough to require breathing machines. The rate of GBS related to the vaccine was about 1 case per million vaccine doses. Since 1976, flu vaccines have not been clearly linked with GBS.

What Other Ways Can H1N1 Be Prevented Besides Vaccination?

  • Wash your hands often, especially when you come in contact with someone who is sick. Wash your hands for 15 to 20 seconds with soap and water. Rubbing alcohol-based cleaners on your hands is also helpful.
  • Avoid close contact with people who have respiratory infections. The flu can spread starting 1 day before and ending 7 days after symptoms appear.
  • Consider using a disposable face mask if you have a high risk of severe illness from the flu and are unable to avoid crowded areas.
  • Cover your mouth and nose with a tissue when you cough or sneeze. Throw away the tissue after you use it. Coughing or sneezing into your elbow or upper sleeve is also helpful.
  • Do not spit.
  • Do not share drinks or personal items.
  • Do not bite your nails or put your hands near your eyes, mouth, or nose.
  • Keep surfaces clean by wiping them with a household disinfectant.
  • Do not use products sold on the Internet claiming to prevent pandemic H1N1 flu. Talk to your doctor before using such products.
  • The CDC recommends that you or your child do not attend swine flu parties.
  • Talk to your doctor about taking antiviral medications.

What Happens in the Event of an Outbreak?

The CDC has issued some specific guidelines for public facilities. This will help schools, businesses, correctional facilities, and healthcare settings manage an outbreak of the flu. The advised actions may include isolating infected individuals and cleaning the facility. In some cases, the facility may need to be closed for a period of time.


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


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Last reviewed September 2018 by David L. Horn, MD, FACP  Last Updated: 9/18/2020