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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, people with some health conditions, or people over age 59. For more information, talk with your doctor or public health nurse.
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.
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.footnote 1
The vaccine is especially important for people who are at higher risk of problems from the flu, including:footnote 1
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? ).
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 (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.footnote 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.
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.footnote 1 But the vaccine is still important for preventing severe illness, complications and death from the flu virus.
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. 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.
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.footnote 1
See Drug Reference for a full list of side effects. (Drug Reference is not available in all systems.)
Some people who are at high risk for complications from the flu can't get a flu shot. 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.footnote 1
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.
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. If you have had GBS, talk to your doctor before getting vaccinated.
You may have to pay for the nasal spray vaccine.
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:footnote 1
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:footnote 1
Complete the new medication information form (PDF)( What is a PDF document? ) to help you understand this medication.
CitationsNational Advisory Committee on Immunization (2014). Statement on seasonal influenza vaccine for 2014–2015. Public Health Agency of Canada. http://www.phac-aspc.gc.ca/naci-ccni/flu-grippe-eng.php. Accessed August 12, 2014.
Current as of: July 12, 2018
Author: Healthwise Staff
Medical Review:E. Gregory Thompson, MD - Internal Medicine & Brian D. O'Brien, MD - Internal Medicine & Adam Husney, MD - Family Medicine & W. David Colby IV, MSc, MD, FRCPC - Infectious Disease
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