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Flu Shot: Facts and Frequently Asked Questions

The "flu shot" is an annual immunization against three strains of the influenza (flu) viruses expected to circulate for that year. The flu shot is safe and it's the most effective way to protect yourself and your family from the flu.


Who should get the flu shot?

All Ontarians should get their flu shot. Unless there is a medical reason not to, everyone aged 6 months or older can benefit from getting the seasonal flu shot.

The following people are at greatest risk from the flu — and are strongly encouraged to get the flu shot:

  • People with weakened immune systems
  • Young children six months to 59 months of age
  • The elderly
  • Pregnant women
  • Family members and those who provide care to people in the groups listed above should also get the flu shot to protect themselves and those around them.
How does the flu shot work?

The flu shot works by prompting your body to build its natural immunity. You get the flu shot, which contains inactive (dead) flu viruses. When your body comes into contact with the flu - even though the strains are inactive, you make antibodies that fight those viruses—even though they are inactive. You're now ready to fight off those flu viruses, using your own natural antibodies. Basically the flu shot, and all vaccinations, help your body build natural immunities by triggering a natural response from your immune system.

Why should I get the seasonal flu shot?
  • Getting a flu shot is the best protection against getting the flu. Studies have found that the flu shot can prevent 70 to 90%* of influenza in healthy adults and children.
  • It reduces the risk of serious flu complications. An Ontario study** showed that every year, the flu shot eliminates 30,000 visits to hospital emergency departments. It also prevents approximately 300 deaths.
  • It's free. Ontario is one of very few places in the world that offer free flu vaccine every year to its residents.

**National Advisory Committee on Immunization (NACI), Statement on Seasonal Trivalent Inactivated Influenza Vaccine (TIV) 2010-2011 ** Kwong JC, et al. 2008

How well does the flu shot protect against the flu?

When there is a good match between the seasonal flu types in the vaccine and the flu types circulating in the community, the flu shot can prevent the flu in about 70% to 90% of healthy children and adults.

For the elderly, studies have shown that flu shots decrease the incidence of pneumonia, hospital admission and death

The flu shot also reduces physician visits, hospitalization and death in high-risk persons less than 65 years of age .

It takes about two weeks after the immunization to develop protection against the flu; protection may last up to one year. People who receive the vaccine can still get the flu, but if they do, it is usually milder.

However, the flu shot will not protect against colds and other respiratory illnesses that may be mistaken for the flu but are not caused by the influenza virus.

When should I get the flu shot?

As soon as possible. The earlier you get it, the sooner you’re protected. Flu activity starts in the fall and typically continues until April. The flu shot is available throughout the season.

How many doses of the flu shot do I need?

One every year. Because the flu virus can change every year, you need protection against the types that circulate each year. Children under 9 years of age who have never had the flu shot require two doses of flu vaccine at least one month apart.

Can the flu shot cause the flu?

No. The vaccine does not contain live viruses so you cannot get the flu from the flu shot.

What are the risks of the flu shot?

The flu shot, like any medicine, is capable of causing side effects. The risk of the vaccine causing serious harm is extremely small. Most people who get the vaccine have either no side effects or mild side effects at the injection site such as soreness, redness and swelling.

Life-threatening allergic reactions are very rare. If they do occur, it is usually within a few minutes to a few hours after receiving the vaccine. Stay at the clinic for 20 minutes after getting your shot, just to be sure. Health care providers at the clinic are trained to monitor and treat these possible reactions.

If you do have a reaction to the flu shot, report it immediately to your health care provider.

What is Guillain-Barré Syndrome (or GBS)?

GBS is a not a very common disease, it causes muscle paralysis and has been associated with certain infectious diseases. The risk of getting GBS from the flu is higher than getting GBS from the flu shot.

Overall, the risk of GBS occurring in association with immunization is small. In comparison to the small risk of GBS, the risk of illness and death associated with influenza is much greater.