Questions about Booster Doses

Why are booster doses of the COVID-19 vaccine needed?

Canada’s National Advisory Committee on Immunization (NACI) has released guidance on booster COVID-19 vaccine doses in Canada with the following objectives: minimize serious illness and death, to preserve health care capacity, and reduce transmission to protect high risk populations.

Booster doses of COVID-19 vaccines can increase the immune response and offer more and longer-lasting protection against infection.


Who should get an initial (first) booster dose of the COVID-19 vaccine?

Individuals 18 years of age and older who have received a primary COVID-19 vaccine series are eligible to get an initial booster dose of an mRNA COVID-19 vaccine (Pfizer Comirnaty® or Moderna Spikevax®) at least 5 ½ months after receiving the second dose in the primary series of the COVID-19 vaccine.

Recently, NACI has recommended an initial booster dose of mRNA COVID-19 vaccine for adolescents 12 to 17 years of age to be received at least 6 months after receiving a primary series of COVID-19 vaccine with the following;

  1. With an underlying medical condition  at high risk of severe illness due to COVID-19 (including those who are immunocompromised and who received a three-dose primary series).
  2. Who are residents of congregate living settings (e.g. shelters, group homes, quarters for migrant workers, correctional facilities).
  3. Who belong to racialized and marginalized communities disproportionally affected by COVID-19.

Adolescents aged 12 to 17 who wish to receive a Pfizer booster dose and who do not fall into the recommended groups above, will be able to receive a booster dose with informed consent.  

Other eligible groups for a booster dose include:

  • Individuals who need to travel internationally for essential reasons (for work or attending school) and received a mixed dose of COVID-19 vaccines can get a matching dose of mRNA vaccine (Pfizer Comirnaty™ or Moderna Spikevax™).
  • Anyone who has received one or two doses of a non-Health Canada authorized vaccine (e.g. Covaxin, Sinovac or Sinopharm) to optimally protect against COVID-19.
  • For essential international travel - Some international countries are not recognizing people as being fully vaccinated if they have received a mixture of COVID-19 vaccines. This has implications for individuals who may need to travel for the purposes of work or attending school. PEI’s Chief Public Health Office allows people who received a mixed dose of COVID-19 vaccines to receive a matching dose of mRNA vaccine (Pfizer Comirnaty™ or Moderna Spikevax™) for the purposes of facilitating international travel (for work or attending school).

A booster dose (2nd dose) of the Janssen (Johnson & Johnson) COVID-19 vaccine may be given to individuals 18 years of age and older at least 2 months after receiving the first dose.

Janssen (J&J) may be administered as a booster vaccine to those who may have a contraindication (for example, an allergy) to an mRNA vaccine or the Novavax NuvaxovidTM vaccine, or any of their components.  For these cases only, NACI recommends that they may be offered viral vector COVID-19 vaccines, including the Janssen (J&J) vaccine, as a booster dose.


Who should get a second booster dose of the COVID-19 vaccine?

Recently, NACI recommended a second booster dose of COVID-19 vaccine for specific populations at higher risk of severe illness and hospitalization from the COVID-19 virus and its variants, including:

  • Individuals living in congregate living settings, including long-term and community care facilities
  • Individuals 60 years of age and older living in the community
  • Indigenous adults 18 years of age and older

Eligible individuals can receive the second booster dose 4 to 6 months after receiving their initial booster dose of the COVID-19 vaccine.

Eligible individuals previously infected with COVID-19 should wait for 3 months after symptom onset or positive test (if asymptomatic) provided it is at least 6 months from completing the primary series or 4 to 6 months from the first booster dose.


Is a booster dose recommended for children under the age of 12?

Currently, a booster dose of the COVID-19 vaccine is no recommended for children under 12 years of age. 


How many doses are recommended for individuals who are moderately to severely immunocompromised?

The National Advisory Committee on Immunization (NACI) has recommended an additional dose of the COVID-19 vaccine for those who are moderately or severely immunocompromisedin order to provide additional protection against the virus.

Those who are moderately to severely immunocompromised will need three doses of vaccine to complete their primary series:

  • active treatment for solid tumour or hematologic malignancies
  • receipt of solid-organ transplant and taking immunosuppressive therapy
  • receipt of chimeric antigen receptor (CAR)-T-cell therapy or hematopoietic stem cell transplant (within 2 years of transplantation or taking immunosuppression therapy)
  • moderate to severe primary immunodeficiency (e.g., DiGeorge syndrome, Wiskott-Aldrich syndrome)
  • Stage 3 or advanced untreated HIV infection and those with acquired immunodeficiency syndrome
  • active treatment with the following categories of immunosuppressive therapies: anti-B cell therapies (monoclonal antibodies targeting CD19, CD20 and CD22), high-dose systemic corticosteroids (e.g. 20 mg/day for ≥ 14 days), alkylating agents, antimetabolites, or tumor-necrosis factor (TNF) inhibitors and other biologic agents that are significantly immunosuppressive.
  • Dialysis patients

5 1/2 months after the completion of the primary series (3 doses), a booster dose of an mRNA COVID-19 vaccine (Pfizer Comirnaty® or Moderna Spikevax®) is strongly recommended.

A 2nd booster dose is recommended 4- 6 months after the 1st booster dose has been administered.


    Where and when can I get a booster dose of the COVID-19 vaccine?

    Residents of long-term care facilities will receive their booster doses at those facilities.

    Individuals who meet the eligibility criteria for a first and/or second booster dose can make an appointment to get a booster dose at either a COVID-19 Vaccine Clinic or a participating pharmacy.

    Moderately to severely compromised individuals should wait at least 28 days after receiving their second dose of the COVID-19 vaccine before receiving a third dose in the primary series.


    I’ve already had COVID-19 and am fully vaccinated, do I still need to get a booster dose? 

    Even if you've already had COVID-19 and recovered, you should still get your booster dose. While you may experience some increase in immunity after being infected with COVID-19, that is not enough to increase your overall immunity over a longer period of time. Getting a booster dose, even after having COVID-19, will provide increased and longer-lasting protection to reduce future infection, community transmission and severe illness.

    If you were recently infected, you can get your first booster dose 3 months after you first experienced symptoms of COVID-19 or since the date of your positive test (and it must be at least 5 ½ months since your second dose before you are eligible for your first booster dose). 

    If you were recently infected and have already received a first booster dose and are now eligible to receive a second booster dose, you should also wait 3 months after you first experienced symptoms of COVID-19 or since the date of your positive test to receive your second booster dose (and it must be at least 4 to 6 months since your first booster dose before you are eligible for your second booster dose).


    Am I still considered “fully vaccinated” if I don’t get a booster dose? 

    Yes, you are still considered fully vaccinated two weeks after getting your second dose in a two-dose series (e.g. Pfizer-BioNTech ComirnatyTM, and Moderna SpikevaxTM, AstraZeneca VaxzevriaTM , Novavax NuvaxovidTM vaccines vaccines), or two weeks after a single-dose vaccine, such as the J&J/Janssen vaccine.


    If we need a booster dose, are the vaccines working? 

    Yes. COVID-19 vaccines are working well to prevent severe illness, hospitalization, and death. However, public health experts are starting to see reduced protection from the primary vaccine series over time against mild and moderate disease, especially among certain high-risk populations. Getting a booster dose at least 5 ½ months after receiving your primary series of the vaccine will increase and extend protection against the virus. 


    How does the booster dose better protect me from COVID-19 variants? 

    Clinical trials show that a booster dose increases the immune response in people who have finished a COVID-19 vaccine primary series 6 months earlier or who received a J&J/Janssen single-dose vaccine 2 months earlier. With an increased immune response, people should have improved protection against getting infected with COVID-19.


    I received the Pfizer-BioNTech ComirnatyTM vaccine for my first two doses, is it safe/effective to get the Moderna SpikevaxTM vaccine for my booster dose(s)? 

    Yes. Either Moderna Spikevax or Pfizer-BioNTech Corminaty vaccines may be used as a booster dose (regardless of which COVID-19 vaccine was used in the primary series).


    Can I receive Novavax Nuvaxovid as a booster dose after receiving a mRNA or viral vector vaccine?

    Yes. Novavax Nuvaxovid can be administered as booster dose to individuals who are unable or unwilling to receive a booster dose of mRNA or viral vector vaccine.


    Are vaccines effective at preventing the spread of the Omicron variant?

    As per a recent statement by the Canadian Council of Chief Medical Officers of Health, “while data remains limited at this time, there is emerging evidence that two doses of a mRNA vaccine are less effective at preventing Omicron infection compared to previous variants but does indicate good protection against more severe disease requiring hospitalization. We also know that a booster dose is a valuable tool to offer protection from infection and do expect that a booster dose will offer very good protection against severe disease. While we do not know how long protection from boosters will last, this is an important tool at this time to help protect our collective progress against COVID-19 and preserve health care system capacity.” The full statement can be found here.


    Published date: 
    June 2, 2022
    Health and Wellness

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