OTTAWA/TORONTO -- Canadian health officials said on Monday they would stop offering AstraZeneca’s COVID-19 vaccine to people under age 55 and require a new analysis of the shot’s benefits and risks based on age and gender.

The moves follow reports from Europe of rare but serious blood clots, bleeding and in some cases death after vaccination, mainly in young women. No such cases have been reported in Canada, with about 307,000 AstraZeneca doses administered.

“We are pausing the use of AstraZeneca vaccine to adults under 55 years of age pending further risk benefit analysis,” Canada’s deputy chief public health officer Howard Njoo said at a media briefing.

Njoo later noted that Canada was taking this “prudent” approach because alternative vaccines are available. Most of Canada’s supply so far has come from Pfizer Inc and Moderna Inc.

The National Advisory Council of Immunization (NACI), an independent expert panel, said the rate that the clotting complication happens at is not yet clear. So far, 40% of people who have developed it have died, but that may fall as more cases are identified and treated early, it said.

“From what is known at this time, there is substantial uncertainty about the benefit of providing AstraZeneca COVID-19 vaccine to adults under 55 years of age,” the council in a written recommendation.

Older people face a greater risk of hospitalization and death from COVID-19, and the complication seems to be more rare in that age group, NACI said, so they can be offered the vaccine “with informed consent.”

Health Canada said in a statement it would add new terms and conditions to the vaccine’s authorizations, including “a requirement that the manufacturers conduct a detailed assessment of the benefits and risks of the vaccine by age and sex in the Canadian context.”

Health Canada said it had been in talks with AstraZeneca, and once it has the requested information, it “will determine if additional regulatory actions are necessary.”

It was not immediately clear how long the assessment might take.

The pause affects both versions of the vaccine approved in Canada: One granted to AstraZeneca Canada, and a second for the Serum Institute of India (SII) - which is manufacturing its own version of the vaccine under license - and its Canadian partner Verity Pharmaceuticals.

Many European countries briefly stopped using the Anglo-Swedish firm’s vaccine while investigating the blood clot incidents earlier this month. Canada continued to administer doses, arguing that the benefits of vaccination outweighed potential risks.

Nearly all countries have since resumed use of the AstraZeneca vaccine. But France broke with guidance from the European medical regulator and said on March 19 it should only be given to people aged 55 or older. France said the decision was based on evidence that the clotting affected younger people.

Canada is expecting another 1.5 million doses of the AstraZeneca vaccine this week from the United States, which has not yet authorized its use. Canada has ordered more than 20 million doses from AstraZeneca and SII.