Statement from the Council of Chief Medical Officers of Health (CCMOH): Update on the Use of COVID-19 Vaccine Boosters and on COVID-19 Vaccines and the Risk of Myocarditis and Pericarditis

Press Release

From: Public Health Agency of Canada

Progress continues across Canada with COVID-19 vaccination campaigns now underway in all jurisdictions for children aged 5 to 11. We know that vaccination, in combination with other public health and individual measures, is working to reduce the spread of COVID-19 and its variants. However, the recent emergence of the Omicron variant is a reminder that the COVID-19 pandemic is not over and that we live in a global community. As Chief Medical Officers of Health, we recognize the importance of global equity in vaccine distribution and the role that inequity plays in the emergence of new variants. While we learn more about this variant, we can help preserve our collective progress by continuing COVID-19 vaccination programs and following the key public health strategies that have been effective in helping to manage this pandemic.

Scientific evidence, evolving data and expert advice continue to inform us on the most effective use of COVID-19 vaccines approved in Canada. NACI recently released updated recommendations on COVID-19 vaccine boosters based on evolving epidemiology and evidence on decreasing protection over time. A complete primary series with an mRNA COVID-19 vaccine continues to be the first recommendation, and should be offered to everyone in the authorized age group without contraindications to the vaccine. NACI now also makes recommendations regarding booster doses for those 18 years of age and over if at least 6 months have passed from their primary series.

Specifically, NACI recommends that booster doses of an mRNA COVID-19 vaccine should be offered to the following populations: adults 50 years of age or older; adults living in long-term care homes for seniors or other congregate living setting that provide care for seniors; adults in or from First Nations, Inuit or Métis communities; recipients of a viral vector vaccine series completed with only viral vector vaccines; and adult frontline health care workers (having direct close physical contact with patients) and maybe offered to adults 18 to 49 years of age.

Completing the two-dose vaccination schedule for all who are eligible remains essential. The primary series offers very good protection against hospitalization and death over the long term, particularly when the second dose is given at least 8 weeks after the first dose. A booster restores protection that may have decreased over time, allowing for more durable protection to help reduce infection, transmission, and in some populations, severe disease. NACI has also reviewed the data on individuals who have had previous infection and continues to recommend they receive a similar schedule to those who have not been previously infected. Vaccination even after infection provides the most reliable and long lasting protection against SARS-CoV 2.

As noted in our previous statement on COVID-19 boosters, provinces and territories will continue to build upon NACI’s advice to strategically implement effective vaccination campaigns in their jurisdictions. We are determined to make the best use of COVID-19 vaccines based on the latest evidence and expert advice to reach our collective goals of minimizing serious illness and overall deaths while preserving health system capacity, and reducing transmission to protect high-risk populations. In the advice to provide boosters for adults living in Canada, we are taking a precautionary approach and ensuring that we protect at-risk populations as well as our health system.

NACI has also released updated guidance on the use of mRNA vaccine based on the most recent surveillance data from Canada, the US and Europe, regarding rare cases of myocarditis and pericarditis following vaccination. To mitigate the risk of myocarditis or pericarditis, which has been found to be somewhat higher for Moderna than Pfizer in adolescents and young adults, NACI recommends that the Pfizer-BioNTech 30 mcg product is preferred for the primary series in those 12 to 29 years of age. An 8-week interval between the first and second dose is recommended, as longer intervals such as this are likely to have less risk of myocarditis than shorter intervals and likely to result in improved protection. NACI has also indicated that the Pfizer-BioNTech 30 mcg product may be preferred for the booster dose in those 18 to 29 years of age. Adolescents and young adults 12 to 29 years of age who have already received one or two doses of the Moderna vaccine more than a few weeks ago do not need to be concerned, as the risk of myocarditis/pericarditis with this vaccine is rare and the adverse event usually occurs within a week following vaccination. Vaccination should not be deferred if the preferred product is not available at the time of vaccination.

Cases of myocarditis and/or pericarditis after mRNA COVID-19 vaccination have been reported in approximately 1 in 50,000 or 0.002% of doses administered. The detection of rare events such as this is a demonstration that our surveillance systems in Canada and globally are effective. Adverse events (side effects) following COVID-19 immunization do occur, and the vast majority are mild and include soreness at the site of injection or a slight fever. Over 60 million doses of a COVID-19 vaccine have been administered to date in Canada, with serious effects remaining very rare (0.011% of all doses administered). Observational studies, including those from Canada, continue to show that both approved mRNA vaccines result in high vaccine effectiveness, particularly against severe disease. Some studies, including those in Canada, suggest that the Moderna vaccine induced a somewhat higher immune response that results in higher effectiveness that may last longer compared to the Pfizer-BioNTech COVID-19 vaccine.

Canada’s Chief Medical Officers of Health welcome NACI’s analysis and thank them for providing their updated recommendations. In our previous statement regarding the risk of myocarditis and pericarditis following COVID-19 vaccination, Chief Medical Officers of Health reflected on the importance of making safety a priority in the careful design of our advice and vaccine programs and we will continue to do just that and communicate findings to the Canadian public. We will continue to use evidence to help design strategies that can reduce risks even further over time.

We realize that individuals in Canada may have questions about the updated recommendations on the use of COVID-19 boosters and mRNA vaccines, depending on their age group, vaccination status and unique circumstances. Individuals should continue to consider the clear benefits of all the vaccines approved for use in Canada in preventing severe illness, hospitalization and death from COVID-19. Individuals should seek information from their health care provider or local public health authorities should they have questions about vaccine products that are best for them.

The benefits of vaccines authorized in Canada continue to outweigh the risks. Infection with the virus that causes COVID-19 is linked to a wide variety of complications that can result in hospitalizations and/or death. Myocarditis is one of the known complications of COVID-19 infection, with much higher risks after infection than after vaccine. Vaccination helps to prevent all these complications and, combined with other public health measures like mask wearing, avoiding crowded spaces, increasing ventilation and physical distancing, can help us enjoy the things we love most. Canada’s Chief Medical Officers of Health continue to encourage all individuals to get vaccinated to protect themselves and those around them.

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.


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