Implementing COVID-19 vaccination in Canada — Vaccine dose interval

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Vaccination is a very important tool to help with the control and long-term management of COVID-19. The availability of safe and effective COVID-19 vaccines is a turning point in the global pandemic. This achievement is a testament to the collaboration among scientists, manufacturers, and governments. Canada’s vaccine regulatory system conducts independent scientific review of vaccines and authorizes their use in Canada only when strict standards for safety and effectiveness have been met. Two vaccines, Pfizer-BioNTech and Moderna, have met these requirements to date and are now available to vaccinate Canadians.

Provinces and territories are in the process of vaccinating Canadians safely and rapidly, as supply becomes available from manufacturers, beginning with groups at greatest risk of severe illness, hospitalization and death, as well as health care providers who care for these high-risk individuals and are key to protecting the integrity of our health care systems. Throughout 2021, vaccine will be offered to increasing groups of people as the vaccine supply grows, ultimately reaching all eligible Canadians.

Since the beginning of the COVID-19 pandemic, our work together as Canada’s Chief Medical Health Officers has relied on understanding how this viral infection is spreading and who is at highest risk of illness, hospitalization and death. This information is the basis on which we are rolling-out vaccines, along with emerging science that informs decisions on the best use of COVID-19 vaccines to turn the tide on the pandemic as quickly as possible. Important questions that will guide our vaccination programs that have yet to be fully answered include the duration of the protection provided by the vaccines and the effects of the vaccine on preventing spread of the COVID-19 virus. We are acting on available data and our decisions are based on achieving the greatest public health benefit for Canada.

Canada, like other countries, is in the midst of a pandemic surge – COVID-19 cases are rising, healthcare system capacity is profoundly stretched in some places, and the risk of severe illness and death is growing. Faced with this reality, along with current constraints in vaccine supply, and the imperative to rapidly vaccinate as many high-risk people as quickly as possible, public health authorities are examining options, including potentially delaying the second doses of the Pfizer and Moderna vaccines. This option is being considered only when necessary in order to give more high-risk people earlier access to vaccine in jurisdictions where the number of cases are rising rapidly and threatening the health care system’s ability to keep up. Extending the interval between the doses maintains the 2-dose requirement approved by Health Canada while allowing some flexibility to more rapidly protect high-risk individuals and their health care providers in areas with surging COVID-19 cases.

The National Advisory Committee on Immunization (NACI) addresses the question of delaying the second dose of vaccine in their updated Recommendations on the use of COVID-19 Vaccines. Within the limitations of currently available data, NACI advises that while the second dose should be given according to the approved schedule if possible, jurisdictions may consider delaying the second dose due to logistic or epidemiologic reasons until further supplies of the vaccine become available, preferably within 42 days (6 weeks) of the first dose.  In their expert view, this interval increase is expected to yield similarly high protection seen with second dose administration at 21 or 28 days after the first dose. This is consistent with recommendations released on January 8, 2021 by the World Health Organization that provides flexibility to extend the dose interval up to 42 days in circumstances of vaccine supply constraint and high disease burden.

Canada’s Chief Medical Officers of Health support NACI’s recommendations. We agree that administration of two doses of the Pfizer and Moderna vaccines must be maintained in line with current evidence and regulatory approvals, and efforts should be made to keep with the manufacturers’ vaccine schedule. The flexibility provided by a reasonable extension of the dose interval to 42 days where operationally necessary, combined with increasing predictability of vaccine supply, support our public health objective to protect high-risk groups as quickly as possible. Further, we are committed to evaluating the impact of extending the dosage intervals, working together to monitor vaccine effectiveness and overall safety, and investigating and reporting any adverse events. We will use these data, along with data from international studies, to guide decisions going forward. Where it is necessary for programs to extend the dose interval beyond 42 days based on specific epidemiology and impacts, those programs must monitor the impact closely and share results regularly to add to the developing evidence base.

As Canada’s Chief Medical Officers of Health, we will continue to work closely together, to adapt our approaches as the situation and science evolve, and provide clear and evidence-based information in order to keep Canadians safe and healthy. Vaccines are a very important strategy to control COVID-19 illness, hospitalizations and deaths. However, other strategies must continue until this pandemic comes under control. As case numbers rise and health system capacity is stretched in many areas, we urge Canadians to protect themselves and others by following public health measures and the advice of the public health authority in your area.

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 most senior Public Health Physician of the First Nations and Inuit Health Branch of Indigenous Services Canada, the Chief Medical Officer from the First Nations Health Authority, and ex-officio members from other federal government departments.

SOURCE Ministry of Health


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