After distributing more than 2.3 million AstraZeneca vaccine doses nationwide, public health officials have so far identified 28 suspected cases of a rare but serious condition called vaccine-induced thrombotic thrombocytopenia (VITT).
Dr. Howard Njoo, Canada’s deputy chief public health officer, said Thursday that 18 of those cases have been verified through testing while 10 more await laboratory confirmation.
VITT is blood clots combined with low levels of blood platelets following immunization.
The report on VITT cases comes after some provinces have suspended the use of the AstraZeneca shot. Alberta, New Brunswick, Nova Scotia, Ontario, Saskatchewan and Quebec have all said they will stop using the vaccine for first doses, at least for now.
In announcing its suspension, Ontario said it now believes the VITT incident rate is roughly 1 in 60,000 shots administered — a rate that is much higher than the figure previously cited by Health Canada.
While the AstraZeneca vaccine has been put on pause in many jurisdictions, Canada continues to procure tens of thousands of doses of this product. COVAX, the global vaccine sharing initiative, delivered 665,000 doses today. Those doses have a three-month shelf life and must be administered by the end of August.
Njoo said Canada will continue to buy enough vaccines to get existing AstraZeneca recipients a second shot.
Early data from the United Kingdom suggest the risk of VITT after second doses of AstraZeneca is likely lower than the risk after first doses.
The vaccine maker recommends at least a 12-week interval between the first and second shot. Canada didn’t start administering AstraZeneca until the second week of March, meaning those patients who got an early dose won’t be due until the end of May for the second booster shot.
Other options could be made available to Canadians based on the results of an ongoing U.K. study.
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