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Learn more about COVID-19 vaccines

Vaccines help your immune system protect you against disease. The approved COVID-19 vaccines are safe and highly effective in preventing serious illness, hospitalization, and death.

Protecting yourself from illness means you can be there for your loved ones, and by getting vaccinated you also help protect your community. When many individuals in a population become immune to a disease, the spread of the virus is slowed down and overall risk is reduced. We call this herd immunity. The safest and most rapid way of achieving herd immunity is through large-scale vaccination. Herd immunity protects those who cannot get vaccinated. In the case of COVID-19 this currently includes babies and children under 16, among others.

COVID-19 vaccines work

These vaccines protect us by causing our immune system to be able to respond quickly and protect us if we are exposed to the real infection. Here’s a bit more information about how the two types of COVID-19 vaccines work:

mRNA vaccines

  • Currently, there are two approved mRNA vaccines, the Pfizer BioNTech and Moderna vaccines. mRNA vaccines give instructions that teach our cells how to make a protein found on the surface of the COVID-19 virus. The presence of the protein (created by our body) triggers an immune response and our bodies make antibodies to fight the infection if the real COVID-19 virus enters our body in the future. 

Viral vector vaccines

  • Currently, there are two approved viral vector vaccines in Canada, the AstraZeneca/COVISHIELD and Janssen (Johnson & Johnson) vaccines. These vaccines use a harmless virus to carry a coronavirus gene into our body. This gene triggers an immune response and our bodies produce antibodies to fight the virus that causes COVID-19. The harmless virus and gene are broken down by our body, but the newly produced antibodies remain and provide protection against future COVID-19 infection.
  • What you need to know about viral vector vaccines (Public Health Ontario)

For more on how vaccines work, please see this short video by Immunize Canada:

Click on the links below for a full list of ingredients for the approved COVID-19 vaccines:

COVID-19 vaccines do NOT contain any of the following: 

The best vaccine for you is the first one you are eligible to receive.

While there are differences between the approved COVID-19 vaccines, each went through rigorous testing and have been proven to safely protect against COVID-19.

When it comes to serious illness, hospitalization, and death, after receiving the full series of the approved vaccines, the current data indicate they provide over 90% protection, which is very high.

As a comparison, all currently approved COVID-19 vaccines are more effective at preventing symptoms of COVID-19 than the annual flu vaccine is at preventing symptoms of flu on a typical year.

For more information, please see this short video by Dr. Samir Gupta, a respirologist (lung doctor) at the University of Toronto:

Evidence about how well the different COVID-19 vaccines work against new strains (also known as variants) of COVID-19 is evolving and is actively being looked at by Canada's National Advisory Immunization Committee (NACI). What we do know is that some strains are more transmissible and cause more severe disease, which makes vaccination all the more important.

There is preliminary evidence that all currently approved vaccines provide good protection against the B.1.1.7 strain (first identified in the United Kingdom). Research is ongoing to determine how well vaccines work against other variants. For more detail see Protection against variants, including variants of concern in the Management options for types of COVID-19 vaccines authorized for use in Canada table produced by NACI.

COVID-19 vaccines are safe

Canada has one of the best vaccine safety programs in the world. All the steps normally taken to make sure vaccines are safe were followed for COVID-19 vaccines.

Side effects can occur, but they are usually short-lived and mild.

Short term side effects of COVID-19 vaccines are similar to those seen with other vaccines and include pain and redness at the site of injection, headache, feeling tired, chills, mild fever, and muscle aches. Younger individuals are more likely to experience short term side effects.

Serious side effects are very rare. If they do occur, they are typically felt minutes to hours after receiving the vaccine. Seek immediate medical attention or call 9-1-1 if you experience any of the following within 3 days of immunization:

  • hives 
  • swelling of the face, mouth or throat 
  • trouble breathing 
  • dizziness and weakness 
  • high fever (over 40C) 
  • Convulsions or seizures

Another rare side effect that has been reported is a risk of serious blood clots, or vaccine-Induced Immune Thrombotic Thrombocytopenia (VITT). For more information on VITT, consult the following resources: 

You should talk to your healthcare provider before getting a COVID-19 vaccine if you suffer from serious allergies (e.g., if you carry an Epipen).

For up to date information on COVID-19 vaccine side effects, including which side effects are most common, see Health Canada’s reported side effects following COVID-19 vaccination in Canada, which is updated weekly.

Safe and effective COVID-19 vaccines were developed quickly due to several factors, including:

  • Significant human and financial resources: Unprecedented international collaboration between scientists, health professionals, governments, and industry generated massive resources and funding that sped up vaccine development. 
  • Existing vaccine technology: The first COVID-19 vaccines to be developed and approved were mRNA vaccines. Because this technology has been around and continuously improved upon since the 1990s it was readily available for use to make COVID-19 vaccines. 
  • Rapid genetic sequencing: The genetic sequence for the virus was discovered and shared internationally only a few weeks after the outbreak was first declared. The genetic sequence was key to starting the vaccine development process.

The review process that ensures vaccines are safe and effective was not compromised in any way. Instead, the vaccine approval process was made more efficient. For example: 

  • COVID-19 vaccines were given priority ahead of other medications and medical technologies awaiting review. 
  • Health Canada began looking at trial information while the trials were still being conducted instead of waiting to review all the information after the trials were complete (usually they wait until trials are complete). There are many steps involved in vaccine testing, and each of these must be carefully reviewed. Starting the review process earlier meant that when all steps had been completed by the vaccine makers, the whole review process could be finished faster.

Health Canada vaccine development and approval infographic.

Vaccine regulatory process in Canada overview by Public Health Ontario.

Once Health Canada has approved vaccines based on how safe they are and how well they work, the National Advisory Committee on Immunization (NACI) makes recommendations on their use in specific populations. Provinces and Territories use these recommendations to make their own decisions on vaccine use.

Evaluation of vaccine safety does not stop once a vaccine has been approved by Health Canada. In Canada, there are systems in place to monitor and investigate serious or unexpected side effects that may be linked to vaccination. In Ontario, monitoring of vaccine safety is achieved through collaboration between many partners, including:

  • Health care providers 
  • Public health units 
  • Public Health Ontario 
  • The Ontario Ministry of Health 
  • Health Canada 
  • The Public Health Agency of Canada 
  • Vaccine manufacturers

For more information on how monitoring for vaccine side effects works, and for statistics on the number and types of side effects that have been reported to date in Canada following COVID-19 vaccination, please visit this Health Canada webpage.

COVID-19 vaccine do NOT cause COVID-19

The approved COVID-19 vaccines do not contain the live virus that causes COVID-19.
For this reason, these vaccines cannot make you sick with COVID-19. Some people experience side effects following immunization. These are generally mild, flu-like symptoms that are short lived and usually indicate that the vaccine is working.

mRNA-based COVID-19 vaccines do NOT cause alterations in DNA

The mRNA (which stands for messenger RNA) in these vaccines is like a cooking recipe. It provides instructions to our cells and then is broken down and eliminated from the body once an immune response and antibodies to fight COVID-19 have been created. Our genetic material (DNA) is contained in the central part of our cells called the nucleus. The mRNA never enters the nucleus, so there is no risk of interaction with DNA.

You should delay getting the vaccine if:

  • You have symptoms of COVID-19. To take our COVID-19 symptom screen, please see Preparing for your appointment
  • You are in isolation because you are either a confirmed case of COVID-19 (with or without symptoms) or were identified as a contact of a person with COVID-19. 
  • You received another (non-COVID-19) vaccine in the past 14 days. 
  • You have ever had a severe allergic reaction (i.e. anaphylaxis) to a previous dose of an mRNA vaccine or to any of its components (including polyethylene glycol). If you are unsure if you are allergic to one of the components in the vaccine, talk to a health care provider.

For more information, including questions to help you determine if you fall into a special patient group who should also speak with their health care provider before getting the COVID-19 vaccine, please see Considerations before Getting the COVID-19 Vaccine.

More information from trusted resources

COVID-19 vaccinations: By the numbers

Keep track of how many people have received their vaccination.

Page last modified: May 4, 2021

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