Last updated: May 11, 2021 

TORONTO — Today, Dr. David Williams, Ontario’s Chief Medical Officer of Health, issued the following statement on the use of the AstraZeneca vaccine in the province:

“Effective today, Ontario will be pausing the rollout and administration of first doses of the AstraZeneca vaccine at this time.

This decision was made out of an abundance of caution due to an observed increase in the rare blood clotting condition, known as vaccine-induced immune thrombotic thrombocytopenia (VITT), linked to the AstraZeneca vaccine. As of May 8, 651,012 doses of the AstraZeneca vaccine were administered with a rate of VITT of 0.9 per 100,000 doses administered. 202,873 doses of the COVISHIELD vaccine were administered with a rate of VITT of 1 per 100,000 doses administered. However, over the last few days, there have been increased reports of VITT, with a rate of 1.7 per 100,000 doses administered. In collaboration with health experts at Public Health Ontario, the Science Advisory Table, and our federal, provincial and territorial partners, we are reviewing the data to consider options for the use of the AstraZeneca vaccine for second doses and more broadly moving forward.

Data from the UK points to a much-reduced risk of VITT in second doses of AstraZeneca, and we look forward to providing more guidance in advance of people’s needing to receive their second dose of the AstraZeneca vaccine.

The decision to pause is also based on the increased and reliable supply of the Pfizer and Moderna mRNA vaccines and the downward trend in cases. We are also seeing early promising results of administering two doses of different vaccines and have asked the National Advisory Committee on Immunization (NACI) to provide direction on the interchangeability of COVID-19 vaccines.

Based on the much higher risks of COVID-19 infection recently observed in Ontario including hospitalization, serious illness and death, we maintain that those who received their first dose with the AstraZeneca vaccine did absolutely the right thing to prevent illness, and to protect their families, loved ones and communities.

The health and safety of Ontarians remains our top priority. Ontarians are encouraged to get vaccinated as soon as they are eligible. The right thing to do to protect yourself and those around you is to get vaccinated with the vaccine you were eligible to receive.”