Interchangeability of COVID-19 vaccines, AstraZeneca vaccine Q&A, and quick reference for second doses

Advisory Alert

June 11, 2021

*Cette information est seulement disponible en anglais.

To: Health Care Providers


Interchangeability of COVID-19 vaccines

This Advisory Alert provides information regarding the interchangeability of COVID-19 vaccines to assist you in your practice and facilitate patient decision-making. Working together, we continue on the path to protect our communities against COVID-19 and facilitate completion of the COVID-19 vaccination series.

Mixed COVID-19 vaccine schedules

The National Advisory Committee on Immunization has provided a statement on the interchangeability of authorized COVID-19 vaccines, while the Public Health Agency of Canada has outlined the particulars on mixed COVID-19 vaccine schedules. In summary, individuals who received a first dose of an mRNA vaccine (Pfizer-BioNTech or Moderna) should be offered the same mRNA vaccine for their second dose. If the same mRNA vaccine is not readily available, another mRNA vaccine can be interchanged to complete the vaccine series. The minimum dosing interval will be determined by the first dose product with  a minimum of 21 days for those who had a first dose of Pfizer-BioNTech and a minimum of 28 days for those who had a first dose of Moderna as per the product monograph.

Individuals who received the AstraZeneca COVID-19 vaccine for their first dose, have two options to discuss with their health care provider when considering their second dose. They can opt for a second dose of AstraZeneca or choose to receive an mRNA vaccine. Both options for second doses are safe, provide strong protection against COVID-19, and will complete the COVID-19 vaccine series. These options were outlined in an Advisory Alert dated June 3, 2021, and information for individuals who received a first dose of the AstraZeneca COVID-19 vaccine has been updated.

Q&A to engage your patients in making an informed decision

The Ministry of Health has developed a Q&A for health care providers answering questions on AstraZeneca COVID-19 vaccine second doses. This Q&A intends to facilitate the decision-making process when discussing with your patients their options to choose to receive either a second dose of the AstraZeneca vaccine or an mRNA (Pfizer-BioNTech or Moderna) vaccine for their second dose. Evidence supporting each of these choices is provided including information on how well each option protects against COVID-19, what we know about the risks associated with each option, and when eligibility for booking will become available. Recommendations may be updated as new evidence emerges.

Quick reference for dose two eligibility and information sheet

The Ministry of Health has made available a Quick Reference on COVID-19 vaccine series second dose eligibility. This highly useful tool outlines dosing intervals according to each vaccine and is organized by population groups, including tentative timelines for second dose booking. This guidance is applicable for all two-dose COVID-19 vaccines in Ontario and is based on current vaccine availability.

The Ministry of Health has also developed a COVID-19 Vaccine Information Sheet to provide additional information to inform conversations with patients as well as provide direction on the administration of second doses.

Additional information and resources

Additional information on vaccine interchangeability is available in our sample medical directives for the Pfizer BioNTech COVID-19 Vaccine  and the Moderna COVID-19 Vaccine.

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.

This item was last modified on April 22, 2024