Updated recommendations on exceptions to extended dose intervals for COVID-19 vaccines

Advisory Alert

June 24, 2021

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To: Health Care Providers


Exceptions to the extended COVID-19 vaccine dosing interval

Exceptions to the extended COVID-19 vaccine dosing interval were last shared in an Advisory Alert dated May 29, 2021. This Advisory Alert provides updated information regarding recommendations from the Vaccine Clinical Advisory Group (VCAG) on new exceptions to extended dose intervals for the COVID-19 vaccines.

Certain groups are eligible to receive a second dose of the COVID-19 vaccine at the product monograph interval (21 days for Pfizer-BioNTech and 28 days for Moderna) while other individuals continue to be eligible to obtain a shorter dose interval based on vaccine supply.

New guidance from the Vaccine Clinical Advisory Group

The Vaccine Clinical Advisory Group (VCAG) recommends additional medical exemptions to the vaccine dosing interval. Individuals with certain health conditions should speak with their treating health care provider to determine the timing of their second dose to complete their vaccine series per the product monograph and optimize immune response. These individuals include:

Groups previously identified for product monograph dosing intervals* continue to be eligible. See more about when all individuals can book their second dose from the Government of Ontario.

Pfizer-BioNTech and Moderna dosing interval and interchanging vaccines

As shared in the June 21 Advisory Alert, interchanging of mRNA vaccines is safe and effective. The interval for the second dose is based on the product monograph of the first dose product. Individuals who received Pfizer-BioNTech for their first dose, must wait a minimum of 21 days between doses. For individuals who received Moderna for their first dose, must wait 28 days before getting their second dose.

The National Advisory Committee on Immunization (NACI) recommends that people who have received a first dose of an mRNA vaccine (Pfizer-BioNTech or Moderna) should be offered the same mRNA vaccine for their second dose if it is readily available (easily available at the time of vaccination without delay or vaccine wastage). If the same mRNA vaccine is not readily available, another mRNA vaccine can be considered interchangeable and should be offered to complete the vaccine series.

Individuals who received a first dose of a viral vector vaccine (e.g., AstraZeneca vaccine), may choose to complete the series with AstraZeneca or an mRNA vaccine. An mRNA vaccine is now preferred as the second dose as recommended by the National Advisory Committee on Immunization (NACI). With informed consent, these individuals can receive a second dose of any COVID-19 vaccine at an interval of 8 to 12 weeks.

All Public Health clinics will offer an mRNA vaccine. The vaccine offered will be dependent on what we have available at the time of the clinic. Information on the planned type of vaccine will be provided in advance of the clinic and at the clinic to help individuals make an informed decision. Clients are encouraged to speak with their immunizer if they have any questions about interchangeability.

Information on obtaining vaccine

Booking through the province

Book online using the provincial booking centre.

By phone

Call 705.674.2299 (toll-free: 1.800.708.2505), between 8 a.m. and 8 p.m., seven days a week.

Walk-in clinic

Individuals who are 70 years and older in 2021, or have received a first dose prior to May 9, 2021, can present to a Public Health led walk-in-clinic.

Pharmacies and primary care

Contact the pharmacy or primary care provider where you received your first dose, by visiting https://covid-19.ontario.ca/vaccine-locations for pharmacy locations and booking information.

For additional information on the COVID-19 vaccines, as well as for specifics on how it is being rolled out locally, please visit Public Health’s COVID-19 vaccine webpage.


Original Signed By

Dr. Penny Sutcliffe
Medical Officer of Health and Chief Executive Officer

NOTE: All Advisory Alerts are found on our website.

*Individuals who continue to qualify for product monograph

Certain groups remain eligible to receive a shorten dose interval.  These individuals include:

This item was last modified on June 25, 2021