Ontario Accelerates Second Doses of AstraZeneca COVID-19 Vaccine
June 14, 2021
TORONTO — The Ontario government, in consultation with the Chief Medical Officer of Health and other health experts, including the Ontario Science Advisory Table, is further accelerating the second dose interval for individuals who received their first dose of an AstraZeneca COVID-19 vaccine to eight weeks, with informed consent, from 12 weeks. With informed consent, individuals can choose between a second dose of AstraZeneca or an mRNA vaccine, at an eight to 12-week interval, recognizing that while waiting 12 weeks helps to ultimately provide more protection, some may choose to receive their second dose sooner to have the increased protection provided by a second dose earlier. All of these options provide protection against COVID-19, including the Delta variant, and have been deemed safe.
This decision is based on emerging clinical evidence about the administration of two doses of different vaccines, as supported by the National Advisory Committee on Immunization (NACI). Evidence from multiple studies indicates that mixing of COVID-19 vaccines (receiving an mRNA vaccine after an AstraZeneca vaccine) at dosing intervals between eight and 12 weeks is safe and demonstrates a beneficial immune response. There is evidence that a longer interval between two doses of the AstraZeneca vaccine (such as a 12-week interval) provides higher protection. Beginning Monday, June 14, 2021 at 8:00 a.m., individuals who received their first dose of the AstraZeneca vaccine will be eligible to book their second dose appointment at an interval of eight weeks or more with informed consent. Individuals who wish to receive an mRNA vaccine for their second dose can book an appointment through