Canada following fears that the Oxford/AstraZeneca Covid-19 vaccine could be related to unusual blood clots suspended its use for people under 55.
The National Advisory Committee on Immunization recommended the pause for safety reasons. The suspension was declared on Monday by the Canadian provinces, which are in charge of health care in the region, reports The Guardian.
Dr Shelley Deeks, vice-chair of the National Advisory Committee on Immunization said, "There is substantial uncertainty about the benefit of providing AstraZeneca Covid-19 vaccines to adults under 55 given the potential risks."
The revised guidelines are focused on recent European evidence that shows the risk of blood clots is now as high as one in 100,000, far higher than the one in one million risk previously assumed, according to Deeks.
She mentioned that the majority of patients in Europe who developed a rare blood clot after receiving an AstraZeneca vaccine were women under the age of 55, with a fatality rate of up to 40% among those who developed clots.
Despite the fact that AstraZeneca was found to have no elevated risk of blood clots in Europe, according to Dr Joss Reimer of Manitoba's vaccine implementation taskforce, an uncommon but very severe side-effect has been seen mainly in young women in Europe.
According to Reimer, the uncommon form of blood clot occurs four to twenty days after taking the injection, and the effects are close to those of a stroke or heart attack.
"While we still believe the benefits for all ages outweigh the risks I'm not comfortable with 'probably'. I want to see more data coming out of Europe so I know exactly what this risk-benefit analysis is," Reimer said.
The AstraZeneca vaccine, which has been approved in more than 70 countries, is a key component of the UN-backed Covax initiative, which aims to bring Covid vaccines to developing countries.
It's also been a crucial tool in European countries' attempts to speed up vaccine rollouts, which have been slow. That makes any questions about the shots all the more troubling.
"This vaccine has had all the ups and downs. It looks like a rollercoaster," said Dr Caroline Quach-Thanh, the chair of the National Advisory Committee on Immunization, when asked if the latest news will lead to further vaccine hesitancy.
There have been no records of blood clots in Canada, according to Health Canada, and the department's chief medical officer, Dr Supriya Sharma, claims the vaccine's benefits outweigh the risks.
The department updated the vaccine's label last week to warn about the rare risk of blood clots.
In Ontario, Canada's most populous province, only those aged 60 and up have earned AstraZeneca.
"We have no concerns with those who have received it so far," said Dr David Williams, Ontario's chief medical officer.
Several European countries that had stopped using the vaccine due to fears that it could trigger blood clots have reintroduced it after the EU's drug regulator declared it effective.
The vaccine is widely used in the United Kingdom, throughout the European continent, and in other countries, but its widespread use has been delayed by contradictory study findings on its efficacy, and more recently, a clot scare that has caused some countries to temporarily suspend vaccinations.
This week, Canada will receive 1.5 million doses of AstraZeneca from the United States.