COVID-19 vaccine update: Fourth doses for select populations

Advisory Alert

January 14, 2021

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To: Local Health System Partners


Expanded eligibility for booster of COVID-19 vaccine

In follow-up to the December 17, 2021 Advisory Alert on booster dose eligibility, this Advisory Alert outlines updated recommendations from the Ontario Ministry of Health Third Dose Recommendations guidance regarding fourth doses among immunocompromised individuals, residents of long-term care homes, residents of retirement homes, and older adults living in congregate settings.

Boosters (fourth doses) for moderately to severely immunocompromised individuals

Immunocompromised individuals who are eligible for a three-dose primary series are eligible for a booster dose (fourth dose) ≥ 3 months (84 days) after completion of the primary series.

The intent of the booster dose is to restore protection that may have decreased over time with the goal of enhancing immune response. Eligible individuals should consult their health care provider for guidance on specific timing of booster dose vaccination.

It also is recommended that everyone who comes into close contact (health care workers, friends, family, etc.) with these individuals get vaccinated to help build a ring of protection.

Per processes previously outlined, these individuals may present to a clinic with proof of eligible prescriptions or a referral form from their health care provider. The previous referral letter from third doses for the primary series can be noted. More information is available in the Ministry of Health Third Dose Recommendations (PDF).

Fourth doses for residents in long-term care and retirement homes, and older adults in congregate settings

Evidence shows that residents of long-term care homes and retirement homes, and older adults living in other congregate settings are at increased risk of contracting COVID-19 infection and experiencing severe illness, hospitalization, and death. Given the timing of their third doses, these individuals are likely becoming increasingly susceptible to infection due to waning immunity.

Fourth doses of an mRNA vaccine are now recommended for residents of long-term care homes, retirement homes, Elder Care Lodges and older adults living in other congregate settings who received their third dose ≥ 3 months (84 days) prior.

Practically, some residents may receive shorter intervals than the recommended ≥3 months (84 days) due to operational considerations when boosting entire facilities. Informed consent will be required to shorten the interval.

Planning is underway with local long-term care homes, retirement homes, and other congregate living settings to help coordinate vaccination for these residents. Long-term care home vaccinations began this week.

For more information on eligibility, review the Ministry of Health Third Dose Recommendations (PDF).

Local Vaccination Opportunities

Please visit our Vaccination clinics for COVID-19 webpage for information on clinic dates, times, and locations. Clients can attend a walk-in vaccination clinic or book an appointment online at or by calling 705.674.2299 (toll‑free: 1.800.708.2505), between 8 a.m. and 6 p.m., Monday to Friday. Clients can also contact a local participating pharmacy or primary care provider.


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.

NOTE: All Advisory Alerts are found on our website.

This item was last modified on January 14, 2022