COVID-19 vaccine update: Recommendations on expanded booster dose and third dose eligibility for individuals aged 50+

Advisory Alert

December 6, 2021

*Cette information est seulement disponible en anglais.

To: Local Health System Partners


Expanded eligibility for booster and third dose of COVID-19 vaccine

This Advisory Alert outlines new recommendations from the Ontario Ministry of Health regarding the expansion of third dose eligibility for the COVID-19 vaccines in follow-up to the Advisory Alert issued November 4, 2021.

On December 2, 2021, the Government of Ontario announced expanded eligibility for third doses of the COVID-19 vaccines and updated their COVID-19 Vaccine Third Dose Recommendations. Starting December 13, 2021, at 8 a.m., individuals 50 years of age and older who received their second dose of COVID-19 vaccine at least 6 months ago (168 days, 24 weeks) will be eligible to book an appointment for a booster dose.

Additionally, starting immediately, individuals receiving dialysis (hemodialysis or peritoneal dialysis) are eligible for a three dose primary series. These individuals are now included with those who are moderately to severely immunocompromised as these populations are at increased risk of severe outcomes from COVID-19 and have demonstrated a sub-optimal immune response to a complete two-dose series. The recommended interval between the second dose and the third dose is at least two months (56 days), with a minimum of interval per the National Advisory Committee on Immunization (NACI) of 28 days.

Re-vaccination with a new vaccine series post transplantation for select individuals

Effective immediately, it is recommended that a re-vaccination with a new COVID-19 vaccine primary series be initiated for the following individuals:

These individuals are eligible for a new series due to the loss of immunity following therapy or transplant. Optimal timing should be determined on a case by case basis in consultation with the clinical team.

Continued eligibility for a third dose of COVID-19 vaccine

The Government of Ontario recommends a third dose (PDF) of a COVID-19 vaccine as part of a primary vaccine series (meaning 3 doses are needed for full immunity). For the full list of those currently eligible, please visit

Those who are moderately to severely immunocompromised should receive their third dose at least 8 weeks following their second dose. Per the National Advisory Committee on Immunization and the Ministry of Health COVID-19 Vaccine Third Dose Recommendations, the minimum interval should be no less than 28 days.

Contact your eligible patients about a third dose

Health care providers are asked to contact their moderately and severely immunocompromised patients regarding third dose eligibility. Per processes outlined in the October 8 Advisory Alert, individuals may present to a Public Health clinic or pharmacy with proof of prescription such as the prescription bottle or prescription documentation. If an individual has a prescription medication not included on the list, they will require a completed referral form (English (PDF)French (PDF)). Individuals may also receive their vaccination on-site at participating primary care provider offices or specialty programs.

Individuals eligible for a third dose of the COVID-19 vaccine should receive a third dose of an mRNA vaccine (Pfizer-BioNTech Comirnaty or Moderna Spikevax). Either Moderna or Pfizer vaccines may be used as a third or booster dose (regardless of which COVID-19 vaccine was used in the primary series) with the Pfizer-BioNTech Comirnaty vaccine recommended for those 12-24 years of age. An mRNA vaccine is also recommended as the best third dose option for individuals that received AstraZeneca/COVISHIELD COVID-19 vaccine for their first and second dose unless contraindicated.

In the event that individuals are unable to receive an mRNA vaccine due to contraindications, they may request a viral vector vaccine and informed consent must be obtained. In this scenario, informed consent must include a discussion about the lack of evidence of an additional dose of a viral vector vaccine in immunocompromised populations as well as potential adverse events.

The Canadian Immunization Guide (Part 3 – Vaccination of Specific Populations) provides guidance for the immunization of immunocompromised persons. Details include timing of vaccination for transplant recipients and those requiring immunosuppressive therapies, including a list of conditions leading to primary immunodeficiency, and information on immunosuppressive therapies. Additional guidance on third dose products and informed consent for viral vector vaccines are including in the Ministry of Health’s COVID-19 Vaccine Third Dose Recommendations guidance document (PDF).

Additional information

For more information on the COVID-19 vaccines, as well as for specific answers to your frequently asked questions visit our FAQ web page or call Public Health Sudbury & Districts at 705.522.9200 (toll-free 1.866.522.9200).


Original Signed By

Dr. Penny Sutcliffe
Medical Officer of Health and Chief Executive Officer

Please note that email addresses of some recipients were provided to Public Health Sudbury & Districts by the College of Physicians and Surgeons of Ontario (CPSO) for the purpose of communications related to COVID-19. If you prefer to no longer receive Advisory Alerts from Public Health, please reply to this email requesting to be removed from our distribution list.

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This item was last modified on December 6, 2021