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 the Health Canada webpage for more information on the side effects of the Pfizer-BioNTech or Moderna vaccines.

Yes. Those who have previously tested positive for COVID-19 should still be vaccinated and people do not need COVID-19 testing prior to vaccination.  

Can the mRNA vaccine alter a person’s DNA?

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.

No. While experts learn more about the protection that COVID-19 vaccines provide under real-life conditions, it will be important for everyone to continue practicing public health measures to help stop the spread of COVID-19. That means covering your mouth and nose with a mask, washing hands often and never touching your eyes, nose or mouth with unwashed hands, staying at least 2 metres (6 feet) away from others and self-isolating when sick.  

How was Health Canada able to approve the COVID-19 vaccine so quickly – did they lower their safety standard for vaccines?

Yes. We want to be able to protect the health of the residents in the LTC homes and so those employees would be eligible to receive the vaccine here in Ottawa.

If a person develops an adverse reaction, what should be done?

No serious safety concerns have been causally linked to COVID-19 vaccines approved in Canada.

If someone experiences an adverse event following immunization, they should report it to a healthcare professional (e.g., family doctor).

An adverse event following immunization (AEFI) is an unwanted or unexpected health effect that happens after someone receives a vaccine, which may or may not be caused by the vaccine.

Healthcare professionals should complete the Adverse Events Following Immunization (AEFI) Form and send it to the local public health unit.

Public health surveillance of AEFIs is important for timely detection of rare vaccine safety issues. For more information visit the OPH page on AEFI reporting.

Expected side effects for each vaccine product are listed on the vaccine product monograph; common side effects could be found under ‘Side effects and risks’.

Who should consult with their family doctor before being vaccinated at the current time because of lack of information from clinical trials (i.e., these individuals were not included in the trials)?

National Advisory Committee on Immunization (NACI) recommends that the COVID-19 vaccine should not be routinely offered to the following populations, who were not included in vaccine clinical trials for the Pfizer BioNTech vaccine, until further evidence is available:

• Under 16 years of age
• Pregnant or breastfeeding /chestfeeding
• Immunosuppressed due to disease or treatment or suffering from autoimmune disorder

However, if a risk assessment by a health care provider deems that the benefits of vaccine outweigh the potential risks for the individual (e.g., where the risk of severe outcomes of COVID-19 and risk of exposure to SARS-CoV-2 is high) or for the fetus/infant (in the case of pregnancy/breastfeeding) and if informed consent includes discussion about insufficient evidence in this population, then a complete series of authorized COVID-19 vaccine may be offered to the following populations:

• Adolescents 12 to 15 years of age
• Pregnant or breastfeeding/chestfeeding
• Immunosuppressed due to disease or treatment or suffering from autoimmune disorder 

What are some precautions that should be considered before receiving the vaccine?

• Delay getting vaccinated if you have a fever or are sick with COVID-19 symptoms.  This helps to avoid attributing any complications from other illness with vaccine-related adverse events, and to minimize COVID-19 transmission at an immunization site
• The National Advisory Committee on Immunization (NACI) recommends that individuals delay pregnancy by at least 28 days after the completion of a two-dose series of mRNA COVID-19 vaccines. Up to date recommendation from NACI can be found here.
• The National Advisory Committee on Immunization (NACI) recommendations support that individuals who are on long-term anticoagulation are not at higher risk of bleeding complications after immunizations and can safely be immunized without stopping their anticoagulation therapy. NACI also recommends that individuals with a bleeding disorder should ensure that their condition is optimally managed before immunization which may require consultation with their treating health care provider.

Has the vaccine been shown to cause Bell’s palsy?

No. A direct connection with the Pfizer BioNTech vaccine and Bell’s palsy, a condition that causes temporary facial paralysis, has not been established. The Pfizer study examined 38,000 patients and found four cases of Bell’s palsy among those who received the vaccine, but this is in keeping with the normal observed incidence of Bell's palsy in the population. The COVID-19 vaccine, like all vaccines, continues to be monitored for adverse events. 

How different is this COVID-19 vaccine from the influenza (flu) vaccine?

No, the Covid-19 and influenza vaccine are separate products. COVID-19 vaccine will not protect you against influenza. The seasonal influenza vaccine changes every flu season. When you receive your annual flu vaccine, you are protected only from the specific influenza strains that are circulating for that given season that are covered by the vaccine.

The Pfizer-BioNTech COVID-19 Vaccine is a vaccine used to prevent COVID-19 disease caused by the SARS-CoV-2 virus. 

What percentage of the population needs to get vaccinated to have “herd immunity”?

Herd immunity is a term used to describe when enough people have protection—either from previous infection or vaccination—that it is unlikely a virus or bacteria can spread and cause disease throughout the population. As a result, on average, the whole population within the community is protected even if some people don’t have any protection themselves. However, isolated or short chains of transmission could still occur. The percentage of people who need to have protection in order to achieve herd immunity varies by disease.

Experts do not know what percentage of people would need to get vaccinated to achieve herd immunity to COVID-19. Some estimates for COVID-19 suggest it may be near 60 to 70%, though the full range of estimates is much broader. While experts learn more about the protection that COVID-19 vaccines provide under real-life conditions, it will be important for everyone to continue practicing public health measures to help stop the spread of COVID-19.

(See also: FAQ: Once a person is vaccinated with the series of two doses of the COVID-19 vaccine, can they stop following public health measures like wearing a mask, physical distancing and self-isolating when they become sick?)