Health Canada has acknowledged a link between AstraZeneca’s COVID-19 vaccine and “extremely rare” blood clots, but says the benefits of using the vaccine still outweigh its risks.
Dr. Supriya Sharma, the agency’s chief medical adviser, told a news conference Wednesday that the decision was made after a “thorough review” of data from Europe and the United Kingdom following reports of a rare type of blood clot in people who had received the vaccine, including the first such instance in Canada reported on Tuesday.
Sharma put the risk of those blood clots — which have been associated with low levels of blood platelets — in context.
For adult women under the age of 45, she said, the risk of a blood clot is about one in 3,300. For women who take birth control pills, she said, that risk jumps to one in 1,600, and if a woman is pregnant, it rises to one in 300. A patient who is hospitalized with COVID-19 has a one in five chance of developing a “serious clot,” she said.
By comparison, Sharma said the risk of a blood clot caused by AstraZeneca is approximately one in 250,000.
By the end of March, more than 20 million doses of AstraZeneca vaccine had been given in the U.K., where there have been 79 reports of blood clots.
“These are extremely, extremely rare,” said Sharma.
Canada has administered more than 484,000 doses of the AstraZeneca vaccine and the Covishield vaccine, which is manufactured in India using the same formula.
Sharma said the sole reported case of vaccine-related blood clotting in Canada so far involved a Quebec woman over the age of 55 who was treated and is recovering at home.
While Health Canada continues to authorize use of the vaccine for people aged 18 and older, the National Advisory Committee on Immunization has recommended that it not be given to anyone under age 55 — advice that Ontario is currently following.
Health Canada reviewed data from the U.K. and Europe and found that while blood clots may be linked to the use of the AstraZeneca vaccine, the benefits of taking it far outweigh the risks.
“Currently, with COVID-19 being very transmissible, there are people who are at high risk of exposure and serious illness,” she said.
“By contrast, there’s a very low risk of experiencing a serious adverse event from this or any of the authorized vaccines.”
Labels for the AstraZeneca vaccine will be updated to include information about the blood clot risk, she said, adding that they “want to make sure that all that information is available.”
“We continue to encourage you to get the first vaccine that is offered to you,” said Sharma.
On Tuesday, the United States paused its use of a COVID-19 vaccine produced by Johnson & Johnson following reports that six women experienced blood clots after getting the shot. More than 6.8 million doses of the vaccine have been administered in the U.S.
Canada has approved the Johnson & Johnson vaccine’s use as well, and has ordered 10 million doses, the first of which are expected to arrive this month.
Kieran Leavitt is an Edmonton-based political reporter for the Toronto Star. Follow him on Twitter: @kieranleavitt