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People line up at walk-in COVID-19 vaccination clinic to receive the AstraZeneca vaccine in Montreal, on April 21.Paul Chiasson/The Canadian Press

Manitoba, Nova Scotia and Newfoundland and Labrador have joined the ranks of provinces no longer offering the Oxford-AstraZeneca COVID-19 vaccine for first doses because of growing concerns over the shot’s link to rare but potentially deadly blood clots.

Health officials across the country are scrambling to deal with reports of severe blood clots, blamed on the vaccine, as new data suggest the risk of the side effect is as high as one in 55,000 in Canada, as opposed to original estimates of one in 100,000.

The Public Health Agency of Canada said Wednesday the country may be experiencing the higher rate of the rare side effect, the first time it has acknowledged the change. The agency said reported cases of the blood clots, called vaccine-induced immune thrombotic thrombocytopenia (or VITT), had increased from 12 to 15 and nine more cases are under investigation. Three people died from the condition.

Meanwhile, British Columbia cited a supply shortage in announcing Wednesday that it would stop using AstraZeneca as a first dose. Saskatchewan has also said it has stopped use of AstraZeneca because of a lack of supply.

Ontario stops first doses of AstraZeneca COVID-19 vaccine

Alberta stops giving first doses of Oxford-AstraZeneca COVID-19 vaccine

The moves to stop administering AstraZeneca, first announced by Alberta and Ontario this week, have left hundreds of thousands of Canadians who received the shot in limbo, as officials consider whether to use the same vaccine or a different one for their second doses.

On Wednesday, the federal government sent provinces the details for their next shipments of the AstraZeneca vaccine – including 250,000 for Ontario alone – but it’s not clear how many provinces will accept them.

Alberta and Ontario both say they have not decided whether they will accept these deliveries. Nova Scotia says it will not. Prince Edward Island is to announce its decision on using AstraZeneca on Thursday, while New Brunswick’s Premier said officials are still weighing their options.

Manitoba said it would accept the next shipment from the federal government and will give people who received their first shot of AstraZeneca the same vaccine for their second dose. Quebec said it is continuing to give AstraZeneca shots, including as a first dose.

Janice Fitzgerald, Chief Medical Officer of Health for Newfoundland and Labrador, said her province will keep some AstraZeneca doses for people who cannot or will not take either of the other two principal COVID-19 vaccines, Pfizer Bio-NTech and Moderna, which are known as mRNA vaccines and not associated with the blood-clot side effect.

“The evidence right now supports using an mRNA vaccine,” Dr. Fitzgerald said.

Robert Strang, Nova Scotia’s Chief Medical Officer of Health, said: “It doesn’t make sense to continue to offer the AstraZeneca vaccine because the mRNA vaccines don’t have the same safety signal.”

On Wednesday, B.C. said that it will stop booking first doses of AstraZeneca because of limited supply. In a statement, Health Minister Adrian Dix and Provincial Health Officer Bonnie Henry did not cite concerns about the blood-clot risk. But they are waiting for findings from studies on using different vaccines for first and second shots and for federal advice to “determine our approach and options for second doses.”

Ontario Health Minister Christine Elliott said Wednesday that future use of AstraZeneca in her province depends on reviews from Health Canada and the National Advisory Committee on Immunization, an independent expert panel that reports to the Public Health Agency of Canada.

Last week, NACI faced heavy criticism over its advice that the mRNA vaccines from Pfizer-BioNTech and Moderna are preferred to the viral vector shots from AstraZeneca and Johnson & Johnson – when the risk of COVID-19 is lower and the wait for an mRNA shot is short.

Since then though there’s been a significant shift with five provinces shelving the vaccine for first doses in part because of the safety concerns.

Ms. Elliott also conceded that a small number of the 50,000 doses Ontario still has on hand, which start expiring in late May and June, could end up unused.

The province is acting “out of an abundance of caution, because the safety and well-being of the people of Ontario has to be our top priority,” said Ms. Elliott, who has herself had a first dose of AstraZeneca.

Ontario health officials say the province is still considering whether it could reduce the four-month gap between doses for AstraZeneca, in order to use up the remaining supply to fully immunize people who have had a first dose. They say they are reviewing data from Britain that suggest the risk of blood clots after the second dose is much lower than for the first dose, at just one in a million. Second doses for those who received AstraZeneca, distributed through pharmacies, are not currently scheduled to start until June.

Ontario also says it is still looking for data from Britain and other countries on whether it is safe and effective to mix different vaccines, which would allow those who received AstraZeneca to have a follow-up dose of Pfizer or Moderna, which are more plentiful in Canada now.

The Public Health Agency of Canada issued a statement Wednesday saying it was up to the provinces to decide “how best to administer” the available vaccines.

Prime Minister Justin Trudeau told the House of Commons Wednesday that based on advice from his doctor, he still plans to get a second shot of AstraZeneca when it is available. However, he did not repeat the message his government has been delivering for months that Canadians should take the first dose they are offered.

In a statement Wednesday, AstraZeneca Canada Inc. noted that drug regulators in Canada, the European Union, Britain and at the World Health Organization have all confirmed the vaccine provides a “high level of protection against all severities of COVID-19.”

“These benefits continue to outweigh the risks,” company spokesman Carlo Mastrangelo said.

However the company’s statement relied on an incidence rate for the severe blood clots based on data up to March 31; provincial governments are relying on more recent risk assessments. AstraZeneca Canada said it estimated that about four in one million people experience the severe side effect. Ontario on Tuesday said the rate based on the latest data was 17 cases of the blood clots per one million vaccines administered.

The Quebec Health Ministry said in a statement Wednesday that fewer than 1,000 doses of AstraZeneca remain from the province’s supply of 411,200 doses, and that it continues to offer it to people aged 45 and older, including as a first dose. The province is waiting for studies on the interchangeability of vaccines before deciding what to do next.

Ontario’s COVID-19 Science Advisory Table released a study this week comparing data from different countries on the side effects of AstraZeneca showing incidence rates of severe blood clots as high as one in 26,500 in Norway, which had five total cases, to one in 127,300 in Australia, which had 11 cases.

With a report from Les Perreaux

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