Drug Information

Influenza Vaccine

Influenza Vaccine


Generic Name Brand Name
trivalent inactivated influenza vaccine (TIV) Agriflu, Fluad, Fluviral, Fluzone, Influvac, Intanza, Vaxigrip
live attenuated influenza vaccine FluMist (nasal)

How It Works

Influenza  (flu), a contagious viral disease, can usually be prevented by getting immunized with a flu vaccine. The inactivated influenza vaccine contains several different strains of killed influenza viruses that are most likely to be circulating within the population in a given year. This vaccine is injected into a muscle, usually in the upper arm. The body develops antibodies to fight off the similar strains of influenza within about 2 weeks.

A flu vaccine (FluMist) that is given as a spray in the nose is also available in Canada. Because this flu vaccine uses live flu virus, it is not recommended for children younger than 2 years, pregnant women, or people with some health conditions. For more information, talk with your doctor.

The vaccine is reformulated every year because the influenza viruses change in ways that make a previous year’s vaccine ineffective. In Canada, the United States, and other temperate areas of the northern hemisphere, flu epidemics usually occur in the winter. To be fully protected, you need to be immunized  each year.

Why It Is Used

The flu vaccine helps protect people from developing influenza infection and its possible complications. In Canada, the National Advisory Committee on Immunization (NACI) suggests that everyone older than 6 months of age get a flu vaccine once a year. Most of the trivalent inactivated influenza vaccines (flu shots) may be used by people who are at least 6 months old. The live attenuated influenza vaccine (nasal spray vaccine) may only be used by people ages 2 to 59. 1

Flu vaccines for children, teens, and adults

The vaccine is especially important for people who are at higher risk of problems from the flu, including: 1, 2

  • People who are age 65 or older. People age 65 or older are the most likely to have problems from the flu.
  • Adults and children who have long-term health problems or impaired or weakened immune systems .
  • People who live in nursing homes or long-term care centres.
  • Women who will be pregnant during the flu season.
  • Children 6 to 59 months of age.
  • Children and adolescents who use long-term ASA treatment.
  • People who are obese with a body mass index (BMI) of 40 or more.
  • First Nations peoples.
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People in a high-risk group travelling to the southern hemisphere from April to September (flu season in that hemisphere) or travelling to the tropics or with organized groups at any time of year should review their vaccination records to determine whether they should get a flu vaccine.

You can keep track of when your child received vaccines using the National Childhood Immunization Record (What is a PDF  document?) or the Alberta childhood immunization record (What is a PDF  document?) .

For the latest updates on influenza immunization policy issues, see the NACI recommendations on the Health Canada website at www.phac-aspc.gc.ca/naci-ccni/index-eng.php.

Close contacts of people in high-risk groups

Close contacts (such as health care workers, family members, and daycare providers) of people who are at high risk for complications of the flu should also be immunized each year with the flu vaccine. 1 This includes those times that the high-risk person has a severely impaired immune system  and is in a protected environment. A protected environment often means the person is hospitalized in an isolated room where staff take extra care to prevent the spread of germs. 3

How Well It Works

How well the flu vaccine works to prevent influenza in part depends on how close the viruses in the vaccine match the flu viruses circulating in the population. A person’s age and the body’s ability to develop antibodies also influence the effectiveness of the vaccine.

When the vaccine contains viruses similar to those circulating in the population, both types of vaccine are about equally effective in preventing the flu. The vaccines prevent the flu in about 70% to 90% of adults younger than 65. Protection is less in people age 65 and older. 1, 3 But the vaccine is still important for preventing severe illness, complications and death from the flu virus.

Side Effects

Serious side effects from the inactivated flu vaccine are extremely rare. The most frequent side effect of the injected vaccine is mild soreness where the injection is given, usually in the upper arm. The soreness is rarely severe enough to interfere with daily activities. 3 The most frequent side effect of the nasal spray vaccine is a stuffy or runny nose.

Because the inactivated flu vaccine (the flu shot) contains killed viruses, it can’t cause influenza. Sometimes a slight fever, muscle aches or pains, and a general feeling of illness develop within about 6 to 12 hours after receiving the immunization and last about 1 or 2 days. These side effects most often occur in young children who have had little to no prior exposure to the flu or the vaccine and have not yet developed antibodies. The side effects are also more likely to occur in people with immune system disorders.

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The live attenuated flu vaccine (the nasal spray vaccine) is made from viruses that do not grow at body temperature, so it does not cause influenza.

The National Advisory Committee on Immunization (NACI) now advises that most people with an egg allergy may safely get the flu shot. But people with an egg allergy should not get the nasal spray vaccine. Anyone who has a severe allergy to eggs, chicken, or any other part of the vaccine should talk with their doctor before getting the vaccine. 1

See Drug Reference for a full list of side effects. (Drug Reference is not available in all systems.)

What To Think About

Who should not get a flu shot

Some people who are at high risk for complications from the flu can’t get a flu shot because they have a severe allergy to eggs or chicken. These people may benefit from taking an antiviral medicine. If you have an allergy to eggs, you may still be able to have the flu shot. But you should not have the nasal spray vaccine. 4

Anyone who has a high fever should not be given the vaccine. The vaccine can still be given if an otherwise healthy person has a minor illness, such as a cold. 5

It is not known whether the flu shot can increase the risk for recurrence of Guillain-Barré syndrome  (GBS) in people with a history of the disease. Usually, the flu shot is only recommended for these people if they are at high risk for severe complications of the flu. 3 If you have had GBS, talk to your doctor before getting vaccinated.

You may have to pay for the nasal spray vaccine.

Priority immunization

Ideally, you should get a flu vaccine every year. In case of a shortage, the NACI recommends that the following people have first priority for receiving the flu vaccine: 1

  • People age 65 and older
  • People ages 2 to 64 who have medical conditions that increase their risk of influenza-related complications
  • Young children between the ages of 6 months and 59 months
  • Health care workers who have direct contact with patients
  • People who live in long-term care facilities
  • Household contacts and out-of-home caregivers of children younger than 6 months of age
  • Pregnant women
  • People who are morbidly obese (BMI of 40 or more)
  • Aboriginal peoples
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People who should not get the nasal spray vaccine

The nasal spray contains a live virus that has been treated so it can’t cause influenza. Because of this, some people should not get the nasal spray, including: 4

  • Children younger than 2 years old.
  • People who have had a serious reaction (anaphylaxis) to flu vaccine in the past.
  • Children and teens ages 2 to 17 receiving ongoing ASA therapy.
  • Pregnant women.
  • People with severe asthma.
  • People who had Guillain-Barré Syndrome within 6 weeks of any prior influenza vaccination.
  • People with a weak immune system .
  • Health care workers who provide care to people with severely weakened immune systems.


Related Information

  • Immunizations
  • Influenza (Seasonal Flu)



  1. National Advisory Committee on Immunization (NACI) (2012). Statement on seasonal influenza vaccine for 2012–2013. Canada Communicable Disease Report, 38(ACS-4): 1–36. Also available online: http://www.phac-aspc.gc.ca/publicat/ccdr-rmtc/12vol38/acs-dcc-4/index-eng.php#Toc324425256.
  2. National Advisory Committee on Immunization (NACI) (2006). Canadian Immunization Guide, 7th ed., pp. 1–372. Ottawa: Public Health Agency of Canada. Also available online: http://publications.gc.ca.
  3. Centers for Disease Control and Prevention (2004). Prevention and control of influenza: Recommendations of the Advisory Committee on Immunization Practices (ACIP). MMWR, 53(RR-6): 1–44. Also available online: http://www.cdc.gov/mmwr/PDF/RR/RR5306.pdf. [Erratum: (2004). MMWR, 53(RR-6): 743. Also available online: http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5332a8.htm.]
  4. National Advisory Committee on Immunization (NACI) (2011). Recommendations on the use of live, attenuated influenza vaccine (FluMist): Supplemental statement on seasonal influenza vaccine for 2011–2012. Canada Communicable Disease Report, 37(ACS-7): 1–77. Also available online: http://www.phac-aspc.gc.ca/publicat/ccdr-rmtc/11vol37/acs-dcc-7/index-eng.php.
  5. Centers for Disease Control and Prevention (2011). Prevention and control of influenza with vaccines: Recommendations of the Advisory Committee on Immunization Practices (ACIP), 2011. MMWR, 60(Early Release): 1–6. Also available online: http://www.cdc.gov/mmwr/pdf/wk/mm60e0818.pdf?source=govdelivery.

Last Revised: August 23, 2013

Author: Healthwise Staff

Medical Review: E. Gregory Thompson, MD – Internal Medicine & Brian D. O’Brien, MD – Internal Medicine & Christine Hahn, MD – Epidemiology