Ontario “pauses” first doses of AstraZeneca
Ontario Chief Medical Officer of Health Dr. David Williams announced late Tuesday afternoon, May 11, that the province will “pause” using AstraZeneca for the first doses of COVID-19 vaccine.
In a statement, the pause was attributed to “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.”
The blood clotting had been occurring on average just under once per 100,000 doses administered, the statement continued as of May 8, after 651,012 doses had been given.
“However, in the last few days, there have been increased reports of VITT, with a rate of 1.7 per 100,000 doses administered.”
The province, public health advisors and science advisors were now reviewing whether AstraZeneca should be used for second, booster doses for those who had already received a first doze of that vaccine.
Data from the United Kingdom indicated a much-lower risk of VITT in second doses of AstraZeneca.
The decision to pause using AstraZeneca was also based on an increasing supply of Pfizer and Moderna vaccines, and the downward trend in COVID-19 cases, Dr. Williams said.
“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.”