Vaccine safety and possible side effects

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Vaccine side effects

Like any medication or supplement (including vitamins), vaccines can cause side effects and reactions.

After being vaccinated, it's common and normal to have temporary side effects. These usually last from a few hours to a few days after vaccination.

This is the body's natural response, as it's working hard to build immunity against the disease. This is called an inflammatory response or reaction.

Most side effects don’t disrupt daily activities. You can take medicine to help with any pain or to lower a fever. Ask your health care provider what they recommend to manage symptoms.

Common vaccine side effects may include:
Symptoms at the injection site, such as: More general symptoms, such as:
  • redness
  • soreness
  • swelling
  • chills
  • fatigue
  • joint pain
  • headache
  • mild fever
  • muscle aches

Children may also be more fussy than usual.

If you or someone in your care experiences any unusual symptoms after vaccination, call one of the following:

Allergic reactions

There's a small chance of a serious allergic reaction to a vaccine, called anaphylaxis. It usually happens shortly after a person receives the vaccine and is treatable.

Your health care provider will ask you to stay at the clinic for at least 15 minutes after vaccination. This is so they can watch for abnormal or very rare reactions (like anaphylaxis) and treat them quickly. Vaccination sites should have a supply of epinephrine to use in case you have an allergic reaction.

Signs and symptoms of anaphylaxis may include:

If you experience any of these symptoms after you’ve left a vaccination site, report it to your health care provider.

Call emergency services right away if you develop any serious symptoms that could be an allergic reaction after vaccination.

Allergies in children

It may be hard to identify anaphylaxis in children who are too young to describe their symptoms. Follow guidance from your health care provider about how long and where to wait after your child is vaccinated. Let them know if your child has any symptoms after vaccination.

Your health care provider will report the reactions to your public health department. These reports are tracked and investigated by your provincial, territorial and federal health authorities. This is so they can determine recommendations for future vaccinations.

Vaccines don't cause autism

Studies have found that vaccines do not cause autism.

It’s unknown exactly why some children develop autism and others don’t. Autism has many possible causes.

Stress-related reactions

Some people who are anxious about vaccines may:

Breathing slowly and deeply, or counting to 10, may help.

Sometimes people can faint during or shortly after receiving a vaccine, and will usually recover within a few minutes. They may remain pale and sweaty, and have low blood pressure for several minutes afterwards.

Fainting has no negative effects on its own, but can lead to head injuries if you fall. Let your health care provider know if you have a history of fainting after getting a vaccine. This will allow them to prepare accordingly.

Stress in children

Young children may experience breath-holding when they’re upset or crying hard. Providing reassurance can help comfort your child.

For more information on how to get ready for your child’s vaccine appointment, consult:

Making sure vaccines are safe

Vaccines must be tested to make sure they’re safe and effective before being approved for use in Canada. Once a vaccine has been approved for use in Canada, it’s monitored for:

Health Canada and the Public Health Agency of Canada share the responsibility for ongoing safety monitoring, which also involves:

Safety monitoring continues even after vaccines are approved for use in Canada.

Learn more about how Canada makes sure vaccines are safe:

Vaccination for COVID-19

Vaccination is one of the most effective ways to protect us against COVID-19. Vaccines will be available at no charge over the course of 2021 to everyone in Canada.

Learn more about:

Types of vaccines

Experts have developed many different types of vaccines to protect us from germs (viruses and bacteria).

Non-live vaccines

This type of vaccine contains killed (inactivated) germs or their parts. It's not possible to develop disease from non-live vaccines, like the injectable polio vaccine.

This is because the killed germ can't reproduce or multiply. However, the body's defence system still recognizes parts of these germs as a foreign body, stimulating an immune reaction.

Non-replicating viral vector vaccines

This vaccine is a type of non-live vaccine that uses a harmless virus as a delivery system. The virus used is not the virus that causes the disease.

Once inside the body, the instructions in the genes teach our cells how to make proteins that will trigger an immune response. Once triggered, our bodies then make antibodies and other immune responses. These immune responses help us fight the infection to prevent us from getting sick. You can’t get a disease from a viral vector vaccine.

mRNA vaccines

mRNA vaccines are a new type of vaccine that don't contain viruses or bacteria. Instead, they contain instructions that teach our cells how to make proteins that will trigger an immune response. Once triggered, our body then makes antibodies and other immune responses.

These immune responses help us fight the infection to prevent us from getting sick.  mRNA vaccines don’t change your DNA.

Live vaccines

Live vaccines, like the MMR (measles, mumps and rubella) vaccine, use live germs that are weakened during the vaccine development process. Live vaccines are very effective because the weakened germs act like a natural infection. They build up the body's immune system without causing the disease.

For example, you could experience some side effects such as fever or pain at the injection site. This shows that the vaccine is working to build your immunity.

Natural immunity and disease prevention

Vaccines help your immune system get ready to protect against a disease without making you sick.

You may become naturally immune after being exposed to a disease. However, the risks of severe complications or even death are much greater than the risks of a severe reaction after getting a vaccine.

For example, if your child gets meningitis naturally, they have a 1 in 10 chance of dying. Those that survive have a 1 in 5 chance of:

An infected person can also spread the disease to others in the community before they show symptoms. Groups at risk include:

Vaccine ingredients

The active components in vaccines are called antigens. Antigens are the parts of germs that teach the body’s immune system to recognize and attack the real germ.

Vaccines also contain small amounts of other ingredients. Each ingredient serves a specific purpose.


The human body naturally produces small amounts of formaldehyde. For instance, an infant's body already contains more formaldehyde than they would receive from a vaccine. 

Formaldehyde is used in some vaccines, such as the hepatitis A vaccine. It's used during the vaccine development process to make germs inactive. The tiny amount of formaldehyde that may be found in vaccines is safe.


Thimerosal breaks down into ethylmercury in the body and quickly leaves the body in the feces. It doesn’t build up in the body or cause health problems (unlike methylmercury, which is found in some types of fish).

Sometimes, many doses of vaccine can be taken from the same vial. Even though each new dose uses a new needle and syringe, thimerosal stops accidental contamination and harmful germs from growing inside the vials.

Thimerosal isn't used in single dose vaccine vials. Routine vaccines in Canada come in single dose vials and are therefore thimerosal-free. Certain flu vaccines come in multi-dose vials and can contain small traces of thimerosal.

Many well-conducted studies have explored thimerosal. During its long history of use in preventing contamination of vaccines, thimerosal has never been found to cause any harm.


Some vaccines include aluminum salts to strengthen the body's immune response to the antigens. This is known as an adjuvant. When administered through vaccines, 50% of the aluminium is eliminated in less than 24 hours. More than 75% is eliminated within 2 weeks.

Aluminum is one of the most common metals found in nature and is present in:

  • air
  • food
  • water

Vaccine Injury Support Program

Canada has very high standards for vaccine safety. Health Canada:

Only vaccines that are proven to be safe, effective and of high quality are approved for use in Canada. As with all vaccines and any medication, there’s a chance that there will be a serious side effect. These are rare, but they do happen.

On June 1, 2021, the Vaccine Injury Support Program, independently administered by Raymond Chabot Grant Thornton Consulting, began accepting applications.

The program provides financial support to you if it’s determined that:

Financial support is also available to you if you’re the dependent or beneficiary of an individual who has died after vaccination.

Supports provided may include:

For more information on eligibility and how to apply, or for program statistics, visit

For individuals vaccinated in Quebec

The Government of Québec will continue to administer its existing Vaccine Injury Compensation Program. Individuals vaccinated in Quebec are required to apply for support through the Government of Quebec’s program.

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