Canadian health officials said they would stop offering AstraZeneca’s Covid-19 vaccine to people aged under 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.

The National Advisory Council of Immunisation (NACI), an independent expert panel, said the rate that the clotting complication happens at is not yet clear. So far, 40 per cent 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 said in a written recommendation.

AstraZeneca said in a statement it respected NACI’s decision and that it was working closely with Health Canada's assessment. The British drugmaker also reiterated that authorities in Britain, the EU as well as the WHO have found the product’s benefits to significantly outweigh the risks across all adult age groups.

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. Older people face a greater risk of hospitalisation 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”.