Statement from the Council of Chief Medical Officers of Health (CCMOH): Interchangeability of Authorized COVID-19 Vaccines


Canada's approach to vaccination has enabled individuals in Canada to protect themselves, their families and communities against severe COVID-19 outcomes and reduce the risk of transmission of the virus. We are seeing increasing vaccine coverage from coast to coast to coast. As Chief Medical Officers of Health, we remain committed to implementing vaccine strategies that bring the greatest benefit to our populations.

We continue to rely on scientific evidence and expert advice to guide our decision-making on the use of authorized COVID-19 vaccines. The National Advisory Committee on Immunization (NACI) has provided updated guidance on the use of mixed vaccine schedules in COVID-19 vaccination programs.

NACI recommends that:

  • For individuals who received a first dose of AstraZeneca/COVISHIELD vaccine (viral vector vaccine), either AstraZeneca/COVISHIELD or an mRNA vaccine may be offered for the second dose, unless contraindicated.
  • For individuals who received a first dose of an mRNA vaccine, the same mRNA vaccine should be offered for their second dose. If the same mRNA vaccine is not readily available or unknown, another mRNA vaccine can be considered interchangeable and should be offered to complete the vaccine series.

NACI's recommendations were informed by current international studies of the safety and immune response produced from mixed vaccine schedules, the rate of severe blood clots with low blood platelets, referred to as Vaccine-Induced Immune Thrombotic Thrombocytopenia (VITT), associated with the use of viral vector vaccines, as well as the current and projected supply of mRNA vaccines.

As Chief Medical Officers of Health, we thank NACI for their analysis and fully support their recommendations. Provinces and territories, informed by NACI and other expert analysis, local epidemiology, and vaccine supply and logistics, will continue to adjust vaccination programs to bring the greatest benefit to our populations.

In Canada, both mRNA and viral vector vaccines are available with sufficient supply to allow choice of second dose for those who had a first dose of AstraZenaca vaccine. Some individuals who started their vaccine series with AstraZenaca/COVISHIELD may want to complete their series with this product; others may prefer to receive an mRNA vaccine for their second dose. Individual decisions should assess risks and benefits based on individual circumstances and preferences. We will ensure that information is provided to support this decision-making.

We are adjusting vaccine dose intervals based on vaccine supply, epidemiology and circulation of variants of concern, population immunity, ongoing monitoring of vaccine safety and effectiveness and operational considerations in our vaccine roll-out strategies. This is consistent with NACI's updated recommendation (May 28, 2021) indicating that, given Canada's current and projected vaccine supply, second doses should be offered as soon as possible, with priority given to those at highest risk of severe illness and death from COVID-19.

Completing the two-dose vaccination schedule remains essential. The first dose offers very good protection against COVID-19 infection, hospitalization and death. The second dose enhances and strengthens that protection over the longer term.

Canada is well on our way to achieving high first dose coverage of COVID-19 vaccines. Having as many eligible individuals as possible fully vaccinated with two doses protects us from future resurgence. Along with continuing to apply public health measures and personal preventive practices we know are effective, vaccination is key to our safe re-opening plans across the country.

As Chief Medical Officers of Health, our goal is to keep everyone in Canada safe and healthy. We will continue to work together to provide clear and evidence-informed public health advice, including on COVID-19 vaccination, as the science and COVID situation in Canada continue to evolve.

The Council of Chief Medical Officers of Health includes the Chief Medical Officer of Health from each provincial and territorial jurisdiction, Canada's Chief Public Health Officer, the Chief Medical Advisor of Health Canada, the Chief Medical Officer of Public Health of Indigenous Services Canada, the Chief Medical Officer from the First Nations Health Authority, and ex-officio members from other federal government departments.

Page details

Date modified: