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Influenza (Flu): The Truth About Vaccines

Girl getting vaccination  

Are vaccines safe? Here are a few facts about vaccines specific to influenza (the flu).

  • The flu is a potentially deadly infection. All government health agencies agree the influenza vaccine (flu shot) is the best way to protect yourself. The flu shot is recommended for all people over the age of 6 months. If you think there is a reason you should not get the flu shot, talk to your doctor. ​
  • When you are vaccinated, you are not just protecting yourself. You are protecting the people around you.
  • Getting the flu shot reduces the chances of the infection being passed from person to person. The more people that are vaccinated, the less the infection will circulate.
  • The flu shot is free in Ontario. Go to for information about coverage in all provinces and territories.

F​ew side effects, some concerns, lots of false information

People who discourage vaccination tend to cite just a few reasons. Some of these concerns about vaccination are valid, most are wrong. People hear advice from many places. Some people wonder what to believe.

The​ concern: The flu is not that bad and not worth the side effects of getting the vaccination.

The evidence: There are some side effects associated with getting a flu shot, mainly soreness, redness and swelling at the injection site. The risk of getting these side effects is less of a concern than the risk of dying or getting serious complications from the flu. Each year about 4000 to 8000 Canadian die from pneumonia due to the flu. Many individuals also develop other serious complications from the flu. In some years, flu illness overloads emergency rooms in Canadian hospitals, resulting in long waiting times for patients to be seen. Overall, the complications from the flu outweigh any potential risk from side effects from the vaccine.

The concern: The flu shot can infect you and make you sick.

The evidence: One thing all vaccines have in common is they do not infect you with the flu. Instead, they provoke an immune response. They trick the body into making antibodies and building a natural immunity against the flu. These antibodies fight the virus without making you sick.

The flu vaccines that are being used in Canada are either made up of flu vaccine viruses that have been ‘inactivated’ and are therefore not infectious, or flu viruses that have been weakened, and therefore cannot cause flu illness. The weakened viruses are cold-adapted, which means they are designed to only cause infection at the cooler temperatures found within the nose. They would not infect the lungs or other areas where warmer temperatures exist.

If a person is exposed to the virus after getting a vaccination, that immune response to the vaccine has already created the antibodies to fight off the virus.

The concern: There is mercury in vaccines that causes autism.

The evidence: Some vaccines use very small amounts of thimerosal. Thimerosal is a mercury–based preservative that contains ethyl mercury. There is also a different form of mercury called methyl mercury. It is known that methyl mercury is found in some aquatic food chains and is concentrated in fish. Methyl mercury can build up in the body and cause neurological problems in children. However, ethyl mercury used in thimerosal is processed differently in the body. It is expelled from the body, not built up.

No credible link between vaccination and autism has ever been found.

The concern: Some pe​ople get sick after getting a vaccination.

The evidence: In 1976, there was an unusually high number of cases of the rare Guillain-Barre Syndrome (GBS) following a swine flu vaccination campaign. There is disagreement about whether the two events were related or a coincidence. The cause of GBS remains unknown. Even if vaccines could cause GBS, the risks are very low. The risk of severe illness from the flu is much higher.

The concern: The flu shot does not work.

The evidence: No vaccination works 100% of the time for 100% of the people who get it. For a vaccine to work effectively, it has to cause the production of the correct antibodies that match the virus. Because the flu virus is constantly changing, it is possible it will change so that the vaccine will not be as effective. To help keep the flu shot effective, every year it is updated with the most common flu viruses of that year. Even if illness occurs, the severity of illness is reduced when a vaccinated person becomes infected.

The concern: If I do get severely ill, modern medical care will save me.

The evidence: Antibiotics, antiviral drugs and ventilators can save the lives of people who get severely ill. However, despite massive medical intervention, people still die from the flu. If you want to rely on modern medicine, get a flu shot. Over the decades, this technology has saved more lives than any other. Some people have forgotten that before vaccination, deadly disease such as smallpox, measles and polio regularly killed or maimed millions.

Questions about th​e flu shot

My baby is too young to get a vaccination. What should I ​do?

It is recommended that babies be older than six months before they get vaccinated for the flu. You can reduce the chance your baby will get infected by having all the baby's caregivers get the flu shot. If everyone in the house stays healthy, chances are the baby will too. You can also not allow others who have not been vaccinated to get too close to your baby.

Can patients w​ho are allergic to eggs receive the flu shot?

Chicken eggs are used in the manufacture of the flu shot. If you can eat an egg without an allergic reaction, it is safe for you to get the vaccine.

However, you should see your doctor before getting the vaccine if:

  • You have had hives or swelling of the lips or tongue after eating eggs
  • You have experienced acute respiratory distress after eating eggs
  • You have a diagnosed hypersensitivity to eggs
  • You have had an allergic reaction to any vaccination before
  • You are allergic to other components of the vaccine. These include: thimerosal, sodium chloride, disodium hydrogen phosphate, potassium dihydrogen phosphate, potassium chloride, formaldehyde, sodium deoxycholate and sucrose.

I already got sick with the flu. Should I still get a shot?

Yes, for three reasons:

  1. The immunity you may have developed when you contracted the flu may not last. A vaccination will further boost any immunity you might have.
  2. The vaccination may protect you from a slightly different strain than the one you already had.
  3. The risk of getting sick (again) far outweighs any small risk from getting the vaccine.
Upton Allen, MBBS, MSc, FRCPC, FAAP​​

World Heath Organization,

Health Canada,




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DeStefano F. Vaccines and autism: evidence does not support a causal association. Clin Pharmacol Ther. 2007 Dec;82(6):756-9. Epub 2007 Oct 10.

Jefferson T, et al. Efficacy and effectiveness of influenza vaccines in elderly people: a systematic review. Lancet. 2005 Oct 1;366(9492):1165-74. Epub 2005 Sep 22.​​