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Third Doses and Boosters


Although evidence continues to show that a complete two-dose COVID-19 vaccine series provides protection against COVID-19 infection and severe outcomes in the general population, immunity wanes over time.

Therefore, as the highly transmissible Omicron variant takes hold in Ontario, cases of Omicron doubling every three days throughout the province, there is an urgent need for a booster dose for everyone who is eligible to receive one, particularly the older population. More information is available on the Omicron and how to stop the spread


The following groups can book their booster dose NOW, with at least a minimum of 84 days after their second dose, to extend their protection due to increased risk of exposure, severe disease and waning immunity:

  • Those 18 years of age or older.  
  • Residents of long-term care homes, retirement homes and First Nation elder lodges, and seniors living in other congregate settings.
  • Anyone aged 50 and over with a previously booked appointment at the 168 day interval can go online or call the Provincial Call Centre to move their appointment up based on the new 84 day interval provided an earlier appointment is available. 
  • Health care workers and designated essential caregivers in congregate settings (including long-term care home and retirement home staff and designated caregivers).
  • Individuals who received two doses of the AstraZeneca vaccine or one dose of the Janssen vaccine. 
  • First Nation, Inuit and Métis adults and their non-Indigenous household members who are 16 years of age or older.

If you are eligible to book an appointment or reschedule an appointment click here.

Third doses are recommended for the following groups to extend their primary series to three doses because they likely did not have as strong of a response to their initial two dose series due to their condition or treatment.

  • Dialysis patients
  • Transplant recipients
  • Those with solid tumours or hematological cancers on active treatment
  • Those who are severe primary immunodeficiency or advanced untreated HIV
  • Recipients of specific immunocompromising medications

Those who have one of these special medical conditions and have not yet received a third dose are strongly encouraged to do so. 

If you are eligible click here for how to book an appointment.

A booster dose is recommended for someone who has completed the original series (first and second dose) to restore full protection of the vaccine that may havedecreased over time.

A third dose is recommended for those who are severely or moderately immunocompromised which may have prevented them from having a strong immune response to their initial two doses of vaccine. Extending their series to a three-dose series is strongly recommended to enhance their immune response.

Science currently tells us:

  • A two-dose series of COVID-19 vaccine provides protection against COVID-19 for most people. However, the immunity protection our bodies make from the vaccines can decrease over time.
  • If the first two doses of vaccines were given at a time interval closer together, the immune protection the body makes may be lower and may decrease faster than if were given at a time interval further apart.
  • Some people may get less immunity protection than others after being fully vaccinated (e.g., people who have certain medical conditions or are receiving certain medical treatments, older adults, people who got a viral vector type of vaccine like AstraZeneca or Janssen).
  • An additional dose of an mRNA COVID-19 vaccine offers an extra layer of protection that will fight against the virus and severe illness rom the Omicron variant.
  • COVID-19 vaccines provide protection against serious illness and death from COVID-19. However, there is evidence that lower vaccine effectiveness has been found in residents of long-term care homes and in older adults, particularly those 80 years of age and over. A booster dose could help restore and maintain protection against infection in those populations.
  • Additional evidence suggests vaccine protection against asymptomatic infection and mild COVID-19 disease may decrease slightly over time. One reason may be the shorter interval between the 1st and 2nd dose. A booster dose could help restore and maintain protection against infection in certain populations.

Early in 2021 Canada’s National Advisory Committee on Immunization prioritized Indigenous Peoples for first and second doses of the COVID-19 vaccine, and is continuing to prioritize Indigenous Peoples for third dose and boosters. Indigenous communities in the region have done a great job of addressing factors that affect COVID-19 vaccination and at reducing the spread of the virus, however Indigenous Peoples across the country have been overly affected by COVID-19 due to several factors.

  • On a local level, some of the earliest vaccines doses were offered to adults from Indigenous communities. This may increase their risk of waning of protection because more time has passed since their second dose and a number of them were vaccinated with a very short interval between doses.
  • On a national level, the rate of active COVID-19 cases started rising in First Nations communities in August 2021 and was 4.2 times higher than the rate in the general population as of October.
  • The number of Canadians who identify as Indigenous and have at least one underlying medical condition connected to severe COVID-19 is higher compared to other Canadians for every age above 20 years of age. This increases the risk of severe outcomes for COVID-19 in the Indigenous population.
  • Because Indigenous People are at greater risk of severe outcomes, access to boosters has the potential to reduce or prevent the exacerbation of intersecting health and social inequities.
  • The risk of spreading the virus is higher in settings where physical distancing and other infection prevention and control measures are challenging, and individuals may not be able to practice precautions to protect themselves from infection.
  • Remote or isolated communities may not have ready access to sufficient healthcare services. Therefore, their risk for severe outcomes, including death, and societal disruption is greater than in other communities.
One of the mRNA (Pfizer or Moderna) vaccines will be used for a third dose or booster regardless of what vaccine you received at your first or second dose. We will do our best to match your doses but both offer the same protection and combining them is safe.

Page last updated: December 20, 2021

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