TORONTO -- As Ontario edges closer to its goal of having 90 per cent of eligible residents fully vaccinated, the Ministry of Health (MOH) has been administering third doses to select populations.

The Ministry is underlining that two doses represent a complete vaccine series and provide strong protection against the virus, including the Delta variant, but are also advising that “for some populations, a third dose may be required as two doses may not provide sufficient protection.”

In August, the MOH began offering third doses to select vulnerable communities. Last month, they expanded that criteria.

An interval of at least two months or eight weeks between the second and third dose is recommended for those eligible. The Ministry says that the minimum interval should be 28 days, but says that “an interval longer than the minimum 28 days between doses is likely to result in a better immune response.”

According to the most recent data, 84 per cent of eligible Ontarians have received two doses of a COVID-19 vaccine, four per cent have received one dose and 12 per cent have not been vaccinated.


The moderate-to-severely immunocompromised population

According to the Ministry of Health, populations that have demonstrated a suboptimal immune response to a complete two-dose COVID-19 vaccine series due to their underlying condition are eligible to receive a third dose of the vaccine.

This includes:

  • Individuals receiving active treatment (e.g., chemotherapy, targeted therapies, immunotherapy) for solid tumour or hematologic malignancies.
  • Recipients of solid-organ transplant and taking immunosuppressive therapy 1Active treatment includes patients who have completed treat
  • Recipients of chimeric antigen receptor (CAR)-T-cell therapy or hematopoietic stem cell transplant (within 2 years of transplantation or taking immunosuppression therapy).
  • Individuals with moderate to severe primary immunodeficiency.
  • Individuals with stage 3 or advanced untreated HIV infection and those with acquired immunodeficiency syndrome.
  • Individuals receiving active treatment with the following categories of immunosuppressive therapies: anti-B cell therapies, high-dose systemic corticosteroids, alkylating agents, antimetabolites, or tumour-necrosis factor (TNF) inhibitors and other biologic agents that are significantly immunosuppressive.

A full list of immunosuppressant medications that render patients eligible for third doses provided by the Ministry can be found here.

Seniors in congregate settings

This includes residents of long-term care homes, retirement homes, elder care lodges, and elderly living in other congregate settings, such as assisted-living facilities, chronic care hospitals and “naturally occurring” congregate retirement settings/congregate seniors apartment buildings, the Ministry said.

Because this subgroup was prioritized when vaccines were first authorized and many completed their vaccination series early, the Ministry states that there has been “more time for waning [efficacy.]”

The recommended interval between the second and third dose for this group is five months, or 20 weeks.

“Vaccines have been effective against COVID-19 in long-term care homes in the 3-4 months after vaccination, but outbreaks are still occurring,” the Ministry said. “In these outbreaks, fully vaccinated residents are being infected, and in some instances leading to severe illness and death.”

“Offering a third dose of a COVID-19 vaccine to this population is intended to help increase protection and prevent outbreaks among this vulnerable population.”

According to the most recent data, there are currently 11 outbreaks in congregate care settings. There have been 21 total in the last month.

The Ministry has not indicting when additional groups will become eligible for third doses. 


Of the two eligible populations, there remains a few exceptions.

According to the Ministry, individuals who have experienced myocarditis or pericarditis following any dose of an mRNA vaccine should defer receiving a third mRNA dose until more information is available.

Individuals who received AstraZeneca/COVISHIELD COVID-19 for their first or second dose will still be eligible to receive a third dose, but it is recommended by the Ministry that the third dose be an mRNA vaccine, unless advised otherwise by a medical professional.


If eligible, residents can obtain their third dose of a COVID-19 vaccine through largely the same avenues that they received their first or second — at a pharmacy, hospital or primary care provider.

The province says that those eligible will be contacted by their health-care provider to confirm their eligibility and provide them with a referral to an available vaccine delivery channel.

“For residents of high-risk congregate settings including long-term care homes, higher-risk licensed retirement homes and First Nations eldercare lodges, third doses will be offered in their residence,” the Ministry said.

The Ministry of Health is asking that residents who think they may be eligible for a third dose to remain patient.

“Please do not contact your health care provider directly.”