Information on COVID-19 Vaccine Third Doses

Third doses are considered part of the initial COVID-19 vaccine series. They are given to enhance the immune response and establish an adequate level of protection for those who are immunocompromised and who may not have developed the best immune response to the first and second dose.  

The third dose is given at least 56 days after the second dose. It will enhance the body’s immune response for better protection. 

If you are not immunocompromised but think you meet the eligibility for a booster dose, visit the COVID-19 Vaccine Booster Doses page.


What’s the difference between third and booster doses?

The type and amount of vaccine given are the same (with limited exceptions) whether you are a receiving a third dose or a booster - the difference is the reason why you are getting this extra dose. 


Who is eligible for a third dose?

If you have questions about your eligibility, please contact the Provincial Vaccine Contact Centre at 1-833-943-3900 (TTY for people who are deaf, hearing-impaired or speech-impaired: 1-866-797-0007), which is open seven days a week from 8 a.m. to 8 p.m. and capable of providing assistance in more than 300 languages.


When am I eligible to get the third dose?

The Ontario recommended interval between the second and third dose is at least 56 days. Discuss the exact timing with your health care provider to optimize the immune response and minimize delays in treating the underlying condition. Third doses are available to those 5 years of age and older who meet the eligibility criteria above. 

NOTE: 12 to 17 year olds who are immunocompromised and are completing their primary series, are eligible for a third dose of adult Pfizer-BioNTech Comirnaty or Moderna Spikevax (with informed consent) vaccine. For an 11 year old turning 12 who received their first dose with the Paediatric Pfizer-BioNTech Comirnaty vaccine, the primary series may be finished with the paediatric formulation.


How do I get my third dose?

Last Updated: 13/01/2022