COVID-19 vaccine update: Ministry of Health updates third dose recommendations

Advisory Alert

November 4, 2021

*Cette information est seulement disponible en anglais.

To: Local Health System Partners


Third (booster) doses now recommended for select populations

This Advisory Alert provides an overview of the updated Ministry of Health COVID-19 Vaccine Third Dose Recommendations following the provincial announcement issued on Wednesday, November 3, 2021. The third dose guidance provides recommendations on booster doses for select populations, dose recommendations for Moderna Spikevax boosters, and an alphabetical list of immunosuppressant medications for third dose eligibility.

This information is subsequent to previous Advisory Alerts outlining third dose eligibility for the moderately to severely immunocompromised, those with eligible prescription medications and, vulnerable elderly living in congregate settings dated September 16, 2021, October 20, 2021, and October 8, 2021, respectively.

Third doses recommendations for primary vaccine series vs. booster doses

On Friday, October 29, the National Advisory Committee on Immunization (NACI) issued Interim guidance on booster COVID-19 vaccine doses in Canada (PDF) outlining recommendations for third doses of the COVID-19 vaccine to boost immunity for those who are at increased risk of waning protection following their primary series, who are at increased risk of severe illness, or who are essential for maintaining health system capacity.

Following NACI’s guidance, the Ministry of Health updated Ontario’s COVID-19 Vaccine Third Dose Recommendations (PDF) to include additional population groups now eligible for a third dose to boost immune response (booster dose) and clarify who continues to be eligible for a third dose in the primary vaccine series.

Third doses as booster doses

Evidence shows that booster doses of mRNA vaccines given at least 6 months after the primary vaccine series elicit a robust immune response. With the potential risk of transmission and the Delta variant widely circulating, booster doses are recommended as added protection in individuals who may experience a waning response and who are more likely to experience severe illness or a high risk of transmission.

Effective Thursday, November 4, 2021, the following groups are eligible for a booster dose of an mRNA COVID-19 vaccine:

Note that while vulnerable older adults living in congregate settings were previously eligible for a third dose at five months from their second dose, the recommended interval is now 6 months in order to align with NACI recommendations.

New eligibility recommendations are made based on current scientific evidence for improved immune response to protect those most at risk. The Ministry of Health and NACI closely follow research on the safety and effectiveness of a third dose and recommendations will be updated as new evidence emerges.

Third doses: primary vaccine series

In addition to those eligible for booster doses, the individuals previously identified for third doses in the primary vaccine series continue to be eligible. This includes:

Moderately to severely immunocompromised individuals should receive their third dose 2 months (8 weeks) after receiving their second dose. Per NACI, the minimum interval for the third dose is 28 days however an interval longer than the minimum is likely to result in a better immune response. Exact timing should be decided with the treating provider in order to optimize the immune response from the vaccine series and minimize delays in management of their underlying condition.

Individuals eligible due to moderate or severe immunocompromising conditions may present to a clinic with a referral form English (PDF)French (PDF) completed by a primary care provider or with proof of prescription vial, receipt, or prescription confirmation. For a list of eligible medications, please see the Clinic Guide to Verifying Immunosuppressive Prescriptions for Third Doses of the COVID-19 Vaccine (PDF). Additional guidance, including an alphabetized medication list, is outlined in the Ministry of Health COVID-19 Vaccine Third Dose Recommendations (PDF).

Third dose recommendations in practice

Either mRNA vaccine (Pfizer-BioNTech Comirnaty or Moderna Spikevax) may be used as a third dose or booster dose regardless of which vaccine product was used in the primary series.

If administering Moderna Spikevax:

Residents of long-term care, retirement homes, and other seniors congregate living, adults 70 years of age and older, and all moderately to severely immunocompromised individuals should receive the full dose (100 mcg) of the Moderna Spikevax vaccine.

For clients less than 70 years of age, a half dose (50 mcg) is recommended if offering Moderna Spikevax as the booster dose.

If administering Pfizer-BioNTech Comirnaty:

If offering Pfizer-BioNTech Comirnaty for a third dose or booster dose, the full dose (30 mcg) is recommended.

Risk/benefit discussion:

Informed consent for all additional doses of the COVID-19 vaccine should include a risk and benefit discussion. Evidence shows booster doses elicit a robust immune response; however, discussions should also not the potential increased risk for myocarditis and pericarditis following receipt of an mRNA COVID-19 vaccine. Additional (booster) doses of the mRNA vaccine should be deferred in individuals who have experiences myocarditis or pericarditis following previous doses of the mRNA vaccine until more information is known.

Additional details on third dose recommendations and requirements are outlined in the Ministry of Health COVID-19 Vaccine Third Dose Recommendations (PDF).

Local vaccination opportunities

Starting Saturday, November 6, 2021, those eligible for a booster dose of the mRNA COVID-19 vaccine can visit to book an appointment.

Appointment and walk-in clinics (no appointment required) are available throughout the Sudbury and Manitoulin districts at Public Health clinics and participating pharmacies, and primary care offices.

Though eligible individuals are strongly encouraged to book an appointment for vaccination, walk-ins will be accepted at Public Health clinics. Clients who choose to attend a walk-in to receive a booster dose of an mRNA COVID-19 vaccine may experience longer wait times.

For a schedule of clinics in the Sudbury and Manitoulin districts, including clinic times and the mRNA vaccine brand that is planned, visit

Additional opportunities being planned

Planning is underway with local partners to finalize additional vaccination opportunities for eligible individuals. More information will be provided directly to homebound clients when they become eligible to receive a third dose in their homes. Additional vaccination opportunities may also be identified for health care workers as they become eligible for a booster dose.

Supporting patient decision-making

As a trusted source of information in our communities, we are asking local health system partners to continue the discussion with patients to ensure that patients have made an informed decision about COVID-19 vaccination. The Quick Reference Tool: COVID-19 Vaccine Minimal Contact Intervention (PDF) provides a user‑friendly format for engaging your patients in discussions around topics such as the safety and importance of the COVID-19 vaccine, vaccination opportunities, along with information dispelling some common misconceptions.

First and second dose coverage remains the focus as a complete COVID-19 vaccine series provides strong protection against COVID-19 infection and severe outcomes. Third doses, while an additional layer of protection, are not urgent.

Additional information

For additional 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

NOTE: All Advisory Alerts are found on our website.

This item was last modified on November 4, 2021