COVID-19 Vaccine

How do mRNA vaccines work?

COVID-19 vaccines use messenger RNA (mRNA) which provides instructions to cells in our bodies to make a viral protein from the coronavirus called a “spike protein”. The mRNA provides the instructions that allow the cell to make the spike protein. Then, the immune system is activated to recognize the spike protein as being different from the body’s own proteins and initiates an immune response. The mRNA is degraded by normal cellular mechanisms and the spike proteins are destroyed by the immune system.

How effective are COVID-19 vaccines?

Two COVID-19 vaccines are currently approved in Canada. Pfizer-BioNTech COVID-19 Vaccine can be given to people 16 years of age and older, including older adults. Moderna COVID-19 Vaccine can be given to people 18 years of age and older, including older adults. In clinical trials, both vaccines were higher than 90% effective. Even after vaccination, it is important to continue practicing public health measures to prevent the spread of COVID-19.

Learn more about the Pfizer-BioNTech and Moderna COVID-19 vaccines.

What are the side effects of the COVID-19 vaccine?

The most frequent side effects are injection site pain, fatigue and headache. Some people receiving the vaccine in trials also reported muscle pain, chills, joint pain and fever. These symptoms were usually mild or moderate in intensity and resolved within a few days after vaccination. These are all expected reactions to vaccines because of the immune response and are very similar to those reported following the seasonal influenza vaccination. Visit Health Canada for more information on the side effects of the Pfizer-BioNTech or Moderna vaccines.

Can people with severe allergies to certain components of the COVID-19 vaccine receive the vaccine?

No. People with a history of severe allergic reaction to a component of the COVID-19 vaccine should not receive the vaccine. 

Visit the Health Canada web page to learn who should not receive the Pfizer-BioNTech or Moderna vaccines.

Can the mRNA vaccine alter a person’s DNA?

No. mRNA can’t alter or modify a person’s genetic makeup (DNA). The mRNA from a COVID-19 vaccine never enters the nucleus of the cell, which is where our DNA are kept. This means the mRNA does not affect or interact with our DNA in any way. Instead, COVID-19 vaccines that use mRNA work with the body’s natural defenses to safely develop protection (immunity) to disease.

Can the vaccine cause a COVID-19 infection?

No. None of the COVID-19 vaccines currently in development use the live virus that causes COVID-19. There are several different types of vaccines in development. The goal of each of the vaccines is to teach the immune system how to recognize and fight the virus that causes COVID-19. Sometimes this process can cause symptoms, such as fever. These symptoms are normal and are a sign of the immune response to vaccine.

It usually takes the body a few weeks to build immunity after receiving a vaccine. It is possible that someone could become infected with the COVID-19 virus before or just after getting the vaccine and get sick. This happens because the vaccine has not had enough time to provide protection in the body. 

Learn more about COVID-19.

Once a person is vaccinated with the series of two doses of the COVID-19 vaccine, can they stop following public health measures?

No. Building immunity takes time. Until vaccines are widely available and while experts learn more about the protection that COVID-19 vaccines provide, it will be important for everyone to continue practicing public health measures to help stop the spread of COVID-19. That means wearing a face covering (mask), washing/cleaning hands often, staying at least 2 metres (6 feet) apart from others and staying home when sick.  

Learn more about preventing the spread of COVID-19.