COVID-19: Vaccine safety and side effects

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Vaccine safety

Only vaccines that are proven to be safe, effective and of high quality are authorized for use in Canada. The COVID-19 vaccines have been rigorously tested during their development and then carefully reviewed by Health Canada.

The vaccines can't give you COVID-19 because they don't contain the virus that causes it. The vaccines also can't change your DNA.

Learn more about vaccine safety in Canada

mRNA vaccines

This type of vaccine provides instructions to your cells for how to make a coronavirus protein. This protein will trigger an immune response that will help to protect you against COVID-19.

Learn more about mRNA vaccines

Viral vector vaccines

This type of vaccine uses a virus that's been made harmless to produce coronavirus proteins in your body without causing disease. Similar to mRNA vaccines, this protein will trigger an immune response that will help to protect you against COVID-19.

Learn more about viral vector vaccines

Common side effects

Side effects after vaccination are often part of the body's natural response to a vaccine. Your body responds this way because it's working hard to build protection against the disease.

Common side effects of COVID-19 vaccination can last from a few hours to a few days, and include:

COVID-19 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. These ingredients are safe and leave the body a few days after vaccination. Some people may be sensitive to specific ingredients, resulting in an allergic reaction.

Each vaccine developed for COVID-19 may have different ingredients. Learn more about the ingredients for the:

Allergic reactions

Allergic reactions are rare, but they do happen and can be severe.

Speak with your health care provider about any serious allergies or health conditions you may have before you get a vaccine.

Contact your health care provider if you experience:

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

Learn more about allergic reactions

Rare reactions that have been reported

As with all vaccines, there's a chance that there will be a serious side effect. All side effect reports, including the rare reactions below, continue to be monitored closely by:

Health Canada is:

mRNA vaccines

Myocarditis and pericarditis

We're aware of reports of reactions following vaccination with mRNA COVID-19 vaccines related to:

  • myocarditis (inflammation of the heart muscle)
  • pericarditis (inflammation of the lining around the heart)

Seek immediate medical attention if you experience any of the following symptoms after getting a vaccine:

  • chest pain or pressure
  • irregular heart beat or rhythm, including too quickly, too slowly or an irregular pattern
  • shortness of breath

International cases indicate that these conditions seem to be occurring more often than expected in some populations and situations, such as:

  • in adolescents and young adults
  • in males
  • following the second dose
  • typically shortly after vaccination
    • symptoms appear to be mild

Evidence is evolving and investigations into the association between myocarditis, pericarditis and mRNA vaccines continue. We’ll continue to monitor this as more:

  • adolescents and young adults are vaccinated
  • second doses are given

Bell’s palsy (facial paralysis)

We’ve seen a number of reports of people developing this rare disorder after receiving a COVID-19 mRNA vaccine. 

Bell's palsy is an episode of facial muscle weakness or paralysis. It begins suddenly and worsens over 48 hours. This condition generally affects nerves on one side of the face.

In very rare cases, Bell’s palsy doesn’t disappear. In the majority of cases, it isn’t permanent.

The symptoms of Bell's palsy may look like other conditions or medical problems. Always see your health care provider for a diagnosis.

Contact your health care provider if you have any of these symptoms:

  • drooling
  • headache
  • tearing from the eye
  • loss of feeling in the face
  • hypersensitivity to sound in the affected ear
  • inability to close the eye on the affected side of the face
  • loss of the sense of taste on the front two-thirds of the tongue
  • mild weakness to total paralysis on one side of the face, affecting facial muscle movement, such as smiling, squinting, blinking or closing the eyelid

Viral vector vaccines

Blood clots with low platelets

Blood clots with low levels of blood platelets that occur after vaccination with viral vector vaccines (AstraZeneca Vaxzevria/COVISHIELD) are rare but serious.

Most serious side effects have been reported up to about a month after vaccination. Quick diagnosis and treatment is critical to reduce the risk of negative outcomes.

Seek immediate medical attention if you experience any of the following symptoms:

  • shortness of breath
  • chest pain
  • persistent abdominal pain
  • blurred vision
  • confusion or seizures
  • severe, persistent or worsening headache
  • skin bruising or tiny blood spots under the skin (sometimes away from the part of your body the needle went in)

Talk to your health care provider about which vaccine is recommended for you. They will take into consideration your risk of:

  • exposure to COVID-19
  • more severe disease or outcomes if you get COVID-19

About the condition

Scientists and doctors are still working to understand this condition. The condition is being referred to as thrombosis with thrombocytopenia syndrome (TTS).

If blood tests are positive for antibodies that affect platelets, this condition is also being called:

  • vaccine-induced immune thrombotic thrombocytopenia (VITT) or
  • vaccine-induced prothrombotic immune thrombocytopenia (VIPIT)

The condition causes thrombosis (blood clotting) and thrombocytopenia (low blood platelet counts). It's different from more common blood clotting issues, such as deep vein thrombosis or pulmonary embolism.

Blood clots can form in different parts of the body, including the brain (called cerebral venous sinus thrombosis) and in the abdomen.


This is a blood clot, which prevents blood from flowing normally.


This is a condition in which you have a low blood platelet count.

Platelets (thrombocytes) are blood cells that help blood clot. Platelets stop bleeding by clumping and forming plugs in injured blood vessels. Low platelets may lead to the bruising which can be seen with this condition.

Capillary leak syndrome

A small number of reports of this rare condition have been reported following vaccination with the AstraZeneca Vaxzevria/COVISHIELD vaccine. Some of the reports reviewed were in individuals who have had this condition previously.

Capillary leak syndrome is very rare, but can be serious. The condition causes fluid leakage from small blood vessels (capillaries). This can result in:

  • low blood pressure
  • swelling, mainly in the arms and legs
  • sudden weight gain

If you have any of the above symptoms in the days after vaccination, you should seek medical attention immediately. You shouldn’t get the AstraZeneca Vaxzevria/COVISHIELD viral vector vaccine if you’ve previously experienced capillary leak syndrome.

Guillain-Barré syndrome (GBS)

We’ve seen a number of reports of people developing this rare disorder after receiving the COVID-19 viral vector vaccine. This number is higher among individuals that received the AstraZeneca Vaxzevria/COVISHIELD vaccine compared to what’s expected in the general population.

Guillain-Barré syndrome is a rare neurological disorder that causes the body’s immune system to damage nerve cells. This can result in:

  • pain
  • numbness
  • muscle weakness, progressing to paralysis in the most severe cases

Most people fully recover from the disorder. Seek medical attention right away if you have any of these symptoms after you get vaccinated. Symptoms can start between 3 and 25 days after vaccination.

Ongoing monitoring of side effects and reactions

As COVID-19 vaccines rollout continues across Canada, safety monitoring is ongoing. The Public Health Agency of Canada, Health Canada, and provincial and territorial health authorities continue to:

Learn about the side effects we're currently monitoring.

As safety issues are investigated, Health Canada will take appropriate action as needed. Reports and investigation of safety concerns show that Canada's vaccine safety monitoring system works.

We encourage anyone who witnesses or experiences a possible reaction to a vaccine to report it to their health care provider.

Health care providers must report possible reactions following vaccination to their local public health authority. The public health authority then reports them to the Public Health Agency of Canada.

Drug manufacturers

Drug manufacturers also have a responsibility to monitor and take action on safety issues. They're required to develop and update a detailed product monograph.

The product monograph provides the necessary information for the safe and effective use of a drug or vaccine. This ensures health care providers and the public are aware of all safety information.

In addition, Health Canada updates a post-authorization activity table regularly for all COVID-19 vaccines and treatments. This table summarizes all activities that happened following approval, including product monograph changes for:

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