Dr. David Williams, Ontario’s chief medical officer of health, said the decision has been made out of an abundance of caution because of increased instances of an extremely rare and potentially fatal blood clotting disorder, vaccine-induced immune thrombotic thrombocytopenia (VITT), linked to the shot.
“We are reviewing the data to consider options for the use of the AstraZeneca vaccine for second doses and more broadly moving forward,” he told reporters Tuesday afternoon.
Williams said the decision was made, in part, because of an “increased and reliable” supply of the Pfizer-BioNTech and Moderna vaccines and a continued downward trend in COVID-19 cases.
In Canada, at least 12 VITT cases have been confirmed out of more than two million doses given and three women have died. In Ontario as of May 8, there were eight VITT cases reported after approximately 901,800 Oxford-Astrazeneca doses were administered.
Dr. Jessica Hopkins, the chief health protection and emergency preparedness officer for Public Health Ontario, said officials “picked up a safety signal” when it comes to a slight uptick in cases of VITT.
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“The vaccine safety system is really working in Ontario and Canada,” she said, reiterating the side effects are rare.
“This is out of an abundance of precaution.”
Hopkins said with COVID-19 cases declining and a slight per capita increase in instances of VITT, she said the safety signal warrants a temporary pause. She said there is currently a one-in-60,000 chance of having some sort of side effect, up from a one-in-100,000 chance.
It’s not clear when the pause on vaccines could be lifted, but officials said there would be advice coming “in the very near future” for those who have already had a dose of the Oxford-AstraZeneca vaccine.
Williams noted data from the U.K. suggests there is much lower risk of blood clots in second doses of AstraZeneca.
“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,” he said.
The Ontario government reported there are 49,280 doses of the shot remaining in the province. Dr. Dirk Huyer, the province’s coordinator of COVID-19 response, said it’s not clear when additional doses might be received from the federal government.
The development came on the same day the Alberta government announced it was going to stop providing first doses of the vaccine.
Alberta Health spokesperson Tom McMillan said since there are no known future shipments of AstraZeneca at this time, a determination was made to utilize the remaining supply as second doses.
This is a developing story that will be updated throughout the afternoon.
— With files from The Canadian Press, Melissa Gilligan and Ryan Rocca