Use of AstraZeneca COVID-19 vaccine in younger adults
As Chief Medical Officers of Health, we take vaccine safety very seriously. In Canada there are mechanisms to investigate and share reports of serious adverse events following COVID-19 vaccination to determine if they are causally linked to COVID-19 vaccines. On March 24, 2021 Health Canada issued a label change and guidance on the AstraZeneca COVID-19 vaccine, following European reports of rare but serious cases of blood clots associated with low levels of blood platelets (i.e., thrombocytopenia) following immunization with the AstraZeneca vaccine. Health Canada will be issuing additional terms and conditions requiring AstraZeneca manufacturers to conduct a detailed assessment of the benefits and risks of the vaccine by age and gender in the Canadian context. This information, along with further international evidence, will be used to determine if additional regulatory actions are necessary.
In the interim, National Advisory Committee on Immunization (NACI) is recommending an immediate pause in the use of the AstraZeneca vaccine in all individuals less than 55 years of age in Canada. This is based on evidence of rare instances of vaccine-induced pro-thrombotic immune thrombocytopenia (VIPIT) following AstraZeneca vaccination reported in Europe, with associated high case fatality and related serious outcomes.
As Chief Medical Officers of Health, we are acting decisively with our unified position to pause the use of AstraZeneca vaccine in Canada in those under age 55 at this time. We are taking this precautionary measure while Health Canada as the regulator completes its updated risk/benefit analysis based on emerging data. During this time of risk assessment, Canada has other vaccine options to address the ongoing risk of COVID-19 infection. To date, such adverse events have not been reported in Canada and AstraZeneca vaccine has not yet been used in large numbers in Canada.
Following population-based analyses of VIPIT, assessing the risk of COVID-19 by age, and considering availability of other vaccines (i.e., mRNA vaccines), from what is known at this time there is substantial uncertainty about the benefit of providing AstraZeneca vaccine to adults under 55 years of age given the potential risks associated with VIPIT. At this time we are pausing the use of AstraZeneca vaccine to adults under 55 years of age, pending further risk/benefit analysis. Adults 55 years of age and older may still be offered the AstraZeneca vaccine, given the increased risk of hospitalization and death due to COVID-19 in this population and since VIPIT reports have been even rarer in that age group. While these reported adverse events have occurred primarily in women, investigations are ongoing as it is possible that more women received the AstraZeneca vaccine making it difficult to assess risk based on sex.
The outcome of VIPIT can be serious, including death. If diagnosed early, VIPIT can be treated and the risk of serious outcomes reduced. Based on current evidence, for those individuals who have already been vaccinated with AstraZeneca for more than 20 days there is no cause for concern. For those who have been vaccinated with AstraZeneca less than 20 days, and anyone vaccinated with the AstraZeneca vaccine going forward, you should seek immediate medical attention in the rare event that you develop symptoms starting four days or more after vaccination, and such as: shortness of breath, chest pain, leg swelling, persistent abdominal pain, sudden onset of severe or persistent worsening headaches or blurred vision, and skin bruising (other than at the site of vaccination). Decisions on the type of second dose that will be offered to those who have been vaccinated with AstraZeneca will be determined based on the latest evidence and research. NACI will review evidence as it emerges to provide advice to public health programs on the potential for completing the vaccine series with other vaccine products. For now, you do not need a second dose for up to 16 weeks from your first dose.
This decision is part of the vaccine safety monitoring and response approach that has long been established in Canada and used to monitor all vaccines, including COVID-19 vaccines. We are responding to this safety signal with the information we have at this time and we will be reviewing new information to inform any changes in our position in the days ahead. Chief Medical Officers of Health are aligned and working closely together to review and act on the latest evidence on safety and effectiveness of COVID-19 vaccines. We will continue to work together to adapt our approaches as the science and situation evolves, and provide clear and evidence-informed guidance in order to keep everyone in Canada safe and healthy.
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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