Health Canada is updating warning labels on AstraZeneca COVID-19 vaccines after concluding that rare but severe blood clots may be linked to use of the vaccine.
A woman in Quebec developed a blood clot after immunization with AstraZeneca’s Covishield vaccine, Canadian health authorities revealed Tuesday.
This was the country’s first domestic report of a clot following immunization with AstraZeneca’s vaccine. Health officials were already investigating reports of similar clots happening in Europe.
The Quebec woman was over age 55 and did not have other risk factors for developing a clot, according to Dr. Supriya Sharma, chief medical adviser with Health Canada, who spoke at a news conference Wednesday. The woman is now recovering at home.
Health Canada still believes the benefits of vaccination with AstraZeneca outweigh the risks, according to Health Canada’s director of the Bureau of Medical Science, Dr. Marc Berthiaume.
“Get whichever vaccine is available to you. The longer you wait to get vaccinated, the longer you’re not protected,” he said at the same news conference. “We know the risk of getting infected and ending up in hospital — that is very real.”
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In Quebec, about 167,000 doses of AstraZeneca’s Covishield vaccine were administered, and one adverse event with a rare clot was observed. That’s in line with data from other jurisdictions, Berthiaume said.
According to Dr. Sharma, the risk of developing a blood clot following immunization with AstraZeneca is about 1 in 150,000. By comparison, the risk of developing a clot while hospitalized with COVID-19 is about one in five.
The vaccine labels have now been updated to include information about the signs and symptoms of blood clots. Those include persistent headache, abdominal pain, pain in limbs, or unusual bruising, Sharma said.
The explained the AstraZeneca-linked clots are caused by immune system stimulation following immunization that leads to platelets being activated and causing clots. Platelets are consumed in the clotting process, so their overall count in the bloodstream goes down.
People who have a history of developing these clots with low platelets should discuss whether or not to take the AstraZeneca vaccine with their doctor, Sharma added. Anyone who does develop a clot following vaccination with AstraZeneca also should not take the second dose, she added.
No specific risk factors have been identified yet that would put someone more at risk of a clot than someone else, according to Health Canada.