Ontario to stop administering first doses of AstraZeneca vaccine over increased concerns of rare blood clots

With the availability of a significant amount of other vaccines in Canada, AstraZeneca Vaccine's future use has become questionable both due to concerns over the increased risk of rare but severe blood clots as well as its unpredictable future supply.

Although Alberta's decision to prioritize mRNA vaccines like Pfizer-BioNTech and Moderna while reserving existing AstraZeneca for second doses was based on a scarcity of supply, Ontario's decision to stop administering AstraZeneca Vaccine as a first dose was made largely due to the rising rate of the blood-clotting condition connected to the shot known as vaccine-induced immune thrombotic thrombocytopenia (VITT).

Williams said that in the past several days there have been a growing number of reports of VITT in Ontario. Out of more than 850,000 AstraZeneca doses given, there are now eight cases in the province as of Saturday at a rate of about one in 60,000 shots administered.

There are growing signs among other provinces and territories that this vaccine will not be prioritized across the country.

(Reporting by Asha Bajaj)