Ontario 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.
The province’s top doctor, Dr. David Williams, made the announcement at a specially-convened press briefing on Friday morning.
According to Dr. Williams, for a limited time during the week of May 24, individuals who received their first dose of AstraZeneca during the period of March 10 to 19 may opt for an earlier dose interval of 10 weeks with informed consent.
Eligible individuals are encouraged to contact the pharmacy or primary care provider where they received their first dose and can book an appointment beginning the week of May 24. This will begin in the regions where the AstraZeneca vaccine was initially launched in pharmacies in March 2021. Primary care settings and pharmacies may also be reaching out to eligible Ontarians, according to a media release issued by the province on Friday.
“Choosing to receive the second dose of AstraZeneca at the 10-week interval is safe and provides strong protection against COVID-19,” Dr. Williams said. “This opportunity is being made available to ensure every vaccine dose possible is used to protect Ontarians during the effective delivery period.”
According to provincial data, nearly one million Ontarians aged 40 and over received the AstraZeneca vaccine as their first dose between March 10 and May 11.
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 said it 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 said it 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.
“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. David 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.”
The province said it is 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.
On May 11, Ontario paused the rollout and administration of first doses of the AstraZeneca vaccine 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. 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.
Ontario is also working closely with health experts to continuously review the data for the use of AstraZeneca for first doses.