Ontario will no longer give the AstraZeneca-Oxford COVID-19 vaccine as a first dose due to the risk of rare blood clots.
Dr. David Williams, chief medical officer of health, said on Tuesday that the province made the decision due to an increase in cases of a rare blood clotting syndrome known as Vaccine-Induced Immune Thrombotic Thrombocytopenia (VITT) linked to the AstraZeneca vaccine.
"Effective today, Ontario will be pausing the rollout and administration of first doses of the AstraZeneca vaccine at this time," Williams told reporters on Tuesday.
Williams said the decision was made out of an abundance of caution. The blood clotting syndrome, while rare, can be fatal.
According to the Ontario health ministry, as of May 8, more than 853,000 doses of the AstraZeneca vaccine were administered with a rate of VITT of roughly 1 per 100,000 doses administered.
The ministry said there have been increased reports of VITT, with a rate of 1.7 per 100,000 doses administered, over the last few days.
Williams said the Ontario government is reviewing the data to consider whether to use AstraZeneca for second doses and is preparing guidance for people who received AstraZeneca as a first dose.Williams said the decision to pause the use of AstraZeneca is also based on an increased supply of the Pfizer and Moderna mRNA vaccines and a downward trend in COVID-19 cases. The province has asked the National Advisory Committee on Immunization (NACI) to provide direction on the mixing and matching of different brands of vaccine for first and second doses.
Ontario has about 50,000 doses of AstraZeneca left.