Ontario will no longer give AstraZeneca COVID-19 vaccine as 1st dose due to blood clot risk

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.

WATCH | Dr. David Williams explains why Ontario is pausing the AstraZeneca vaccine for first doses:

Ontario won't give AstraZeneca vaccine as 1st dose

4 years ago

Duration 1:32

Dr. David Williams, Ontario’s chief medical officer of health, said the province made the decision due to an increase in the rare blood clotting condition linked to the vaccine.

Dr. Jessica Hopkins, the chief health protection and emergency preparedness officer with Public Health Ontario, said there have been eight cases of VITT in Ontario as of May 8, 2021. She said the rate has gone from one in 100,000 to one in 60,000.

Hopkins said the vaccine safety system picked up what she called "safety signals" about AstraZeneca. In the system, vaccine providers report what are known as adverse effects following immunization to public health units, which then report the events to Public Health Ontario. The provincial agency, in turn, reports the events to the Public Health Agency of Canada.

"That's what has allowed us to identify the safety signals," she said.

"When you look at risk on a population level, what we're really looking at is, overall, does this safety signal give us enough concern that we would preferentially choose other products at this point in time? And given that we're seeing the overall case numbers of COVID going down and an increase in the safety signal at a population level, it makes sense to pause Astrazeneca because the risk of severe outcomes with VITT shouldn't be underestimated."

Dr. Dirk Huyer, coordinator of the provincial outbreak response, said VITT is considered serious.

"This is a serious side effect that could lead to serious health implications and potentially to people passing," Huyer said.

Those who got AZ as 1st dose did 'right thing,' official says

In a statement on Tuesday, Williams said data from the United Kingdom points to a much-reduced risk of VITT in second doses of AstraZeneca. The risk of VITT in second doses of AstraZeneca is about one in a million.

"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," Williams said in the statement.

In Canada, at least 12 cases of VITT have been confirmed out of more than two million doses given and three women have died.

Ontario, along with others, is awaiting results of a clinical trial in the United Kingdom looking at giving a different vaccine for the second dose. That would allow people who got AstraZeneca first to be given Pfizer or Moderna for their second dose.

Earlier on Tuesday, the Alberta government announced that it has stopped administering first doses of the AstraZeneca vaccine in favour of other brands because supply of the vaccine is expected to become scarce. 

Vaccine Hunters Canada, a non-profit organization that is "helping eligible Canadians find vaccines" during the pandemic, said on Tuesday that it will take the pause on AstraZeneca for first doses in Ontario seriously.