The Canadian provinces of Alberta and Ontario said on Tuesday they would stop offering first doses of AstraZeneca’s Covid-19 vaccine, with Ontario citing evidence that the risk of rare blood clots is somewhat higher than previously estimated.
Alberta said it took the same step only because it was unclear when more shipments of the vaccine might arrive, and not due to concern about side effects, Reuters reports.
Officials in Ontario said roughly one in 60,000 people who received the vaccine in the province, eight in total, developed the complication, which involves blood clots accompanied by a low level of platelets, cells in the blood that help it to clot.
Regulators and expert groups in Canada, Australia, the United Kingdom and Europe had previously estimated that the risk was between one in 95,000 and one in 130,000.
Ontario’s chief medical officer David Williams said:
We maintain that those who received their first dose with the AstraZeneca vaccine did absolutely the right thing to prevent illness and protect their families, loved ones and communities.
Three deaths in Canada have been linked to the AstraZeneca vaccine.
Officials said the vaccine is effective, and noted that alternative vaccines from Pfizer and Moderna are increasingly available. Canada has distributed just over 20 million doses of various COVID vaccines, and 11.6% were AstraZeneca’s vaccine.
Experts have said it is likely fine to mix COVID-19 vaccines, and a trial underway in the UK is looking at the question directly.