TORONTO, Canada — The Ontario government, in consultation with the chief medical officer of health, Dr David Williams, and other public health experts, is proceeding with second dose administration of the AstraZeneca COVID-19 vaccine, beginning with those who received their first dose of the vaccine between March 10 and March 19, 2021.
On May 11, 2021, following the advice of Ontario’s chief medical officer of health, Dr Williams, the province paused the rollout and administration of first doses of the AstraZeneca vaccine. The decision was made out of an abundance of caution due to an observed increase in an adverse reaction, known as vaccine-induced immune thrombotic thrombocytopenia (VITT), linked to the AstraZeneca vaccine. Ontario is working closely with health experts to continuously review the data for the use of AstraZeneca for first doses. The decision to pause was also based on the increased and more reliable supply of the Pfizer and Moderna mRNA vaccines and the downward trend in cases.
For a limited time during the week of May 24, individuals who received their first dose of AstraZeneca during the period of March 10, 2021 to March 19, 2021 may opt for an earlier dose interval of 10 weeks with informed consent. Choosing to receive the second dose of AstraZeneca at the 10-week interval is safe and provides strong protection against COVID-19. This opportunity is being made available to ensure every vaccine dose possible is used to protect Ontarians during the effective delivery period.
“Nothing is more important than the health of Ontarians, and for the best protection against COVID-19 it is vital that everyone who received the AstraZeneca vaccine for their first dose receives a second dose of a COVID-19 vaccine,” said Dr Williams. “We are providing these individuals with a safe option based on the available data and evidence and will continue to work with Health Canada to monitor the quality and efficacy of all COVID-19 vaccines being used in Ontario.”
Nearly one million Ontarians aged 40 and over received the AstraZeneca vaccine as their first dose between March 10, 2021, and May 11, 2021.
Data from the UK strongly suggests a much-reduced risk of VITT in second doses of AstraZeneca – one in 600,000. Based on this evidence, the province is committed to ensuring Ontarians who received the AstraZeneca vaccine for their first dose, and who do not receive their second dose at the 10-week interval during the week of May 24, will have the ability to receive a second dose of AstraZeneca within the recommended interval of 12 weeks.
The province is working with primary care providers and pharmacies to ensure second dose appointments are scheduled in advance of the 12-week interval, and will provide further information on how individuals who received their first dose of AstraZeneca can book a second dose appointment in the near future.
The province is also looking closely at available data and evidence from a clinical trial in the UK evaluating the administration of two doses of different vaccines and has requested direction from the National Advisory Committee on Immunization (NACI). At this time, NACI does not recommend that vaccines of different types (e.g., mRNA vaccine and viral vector vaccine) be used in the two-dose series, as data on the immune response following mixed vaccine schedules are not yet available. Further information from clinical trials and NACI’s recommendation are anticipated to be available in June 2021.
The province will provide further guidance with respect to administering doses of two different vaccines in the near future and in advance of the 12-week interval when most people are needing to receive their second dose of the AstraZeneca vaccine. When the time comes to receive a second dose, everyone who received a first dose of the AstraZeneca vaccine will receive either an AstraZeneca or mRNA vaccine for their second dose.
As more Ontarians receive a first dose of the COVID-19 vaccine, with over 7.7 million doses administered to date, providing the second dose of the vaccine will offer the best protection possible against COVID-19 and variants, and support provincial vaccination targets as part of Ontario’s Roadmap to Reopen.
