Questions about Third Doses (Boosters)

Why is a third or booster dose 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 protection against infection.


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

Members of the following groups who have received a primary COVID-19 vaccine series are strongly recommended to get should receive a booster dose of an mRNA COVID-19 vaccine (Pfizer Comirnaty® or Moderna Spikevax®) at least 5 1/2 months after the administration of the second second dose:

  • Adults 18 years of age and older

The following groups are at highest risk for hospitalization and are strongly recommended to get a booster dose at 5 1/2 months after the administration of the last dose of vaccine:

  • Residents of long-term care and community care facilities 18 years of age and older
  • moderately to severely immunocompromised individuals who are moderately to severely immunocompromised (after the primary series of three doses)
  • Adults age 50 and older
  • Indigenous peoples 18 years of age and older
  • Health care workers with direct in-person patient contact (regardless of the interval between the 1st and 2nd doses);
  • Individuals 18 years of age and older who received two doses of the AstraZeneca Vaxeveria™ vaccine or one dose of the Janssen vaccine

Other eligible groups for third doses 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).

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.

For those who are moderately to severely immunocompromised in the authorized age group who have not yet been immunized, a primary series of three doses of an authorized mRNA vaccine should be offered.

For those who are moderately to severely immunocompromised in the authorized age group who have previously received a 1- or 2-dose COVID-19 vaccine series (with a homologous or heterologous schedule using mRNA or viral vector vaccines), an additional dose of an authorized mRNA COVID-19 vaccine should be offered; this applies to individuals with the following conditions:

  • 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

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.

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.


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

    Residents of long-term care facilities will receive their third dose at those facilities.

    Individuals who meet the eligibility criteria can now make an appointment to receive the third dose of the vaccine at either a COVID-19 Vaccine Clinic or from 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. Everyone else who is eligible should wait at least 5 1/2 months after receiving their second dose before receiving a third dose.

    Published date: 
    January 20, 2022
    Health and Wellness

    General Inquiries

    Department of Health and Wellness
    4th Floor North, Shaw Building
    105 Rochford Street
    Charlottetown, PE   C1A 7N8

    Phone: 902-368-6414
    Fax: 902-368-4121

    DeptHW@gov.pe.ca