Health·Second Opinion

Canada monitoring guidance on AstraZeneca-Oxford vaccine amid potential link to blood clots

Scientists in Europe have reportedly found a link between the AstraZeneca-Oxford COVID-19 vaccine and extremely rare but potentially fatal blood clots, but Canadian public health officials have so far provided no update on guidance for the shot.

Reported connection between COVID-19 vaccine, rare blood clots could affect rollout

Researchers in Germany and Norway have reportedly found a mechanism that could cause the AstraZeneca-Oxford vaccine to create blood clots in very rare circumstances. The finding has renewed debate over the COVID-19 vaccine's benefits and possible risks. (Benoit Tessier/Reuters)

This is an excerpt from Second Opinion, a weekly roundup of health and medical science news emailed to subscribers every Saturday morning. If you haven't subscribed yet, you can do that by clicking here.


Scientists in Europe have reportedly found a link between the AstraZeneca-Oxford COVID-19 vaccine and extremely rare but potentially fatal blood clots, but Canadian public health officials have so far provided no concrete update on guidance for the shot.

News broke on Friday that researchers in Germany and Norway said they had found a mechanism that could cause the AstraZeneca-Oxford vaccine to create the blood clots in very rare circumstances, in addition to identifying a possible treatment for it.

The finding comes after the European Medicines Agency (EMA) investigated 25 cases of the rare blood clots out of about 20 million AstraZeneca shots given and concluded on Thursday that the benefits from the vaccine far outweigh its possible risks, although a definitive link could not be ruled out.

The EMA said there was no increased risk from blood clots and that because the AstraZeneca-Oxford vaccine is effective in preventing COVID-19, which itself causes blood clots, the shot could actually reduce the risk of them overall.

But not all blood clots are the same, and 18 of the cases in Europe were of an extremely rare type called cerebral venous sinus thrombosis (CVST) — where veins that drain blood from the brain are obstructed and can potentially cause fatal bleeding.

Most of the incidents occurred within 14 days of receiving the AstraZeneca shot, and the majority were in women under the age of 55. It's worth noting that this type of blood clot is much more common in women, particularly during and after pregnancy and while on birth control.

WATCH | Tam says benefits of AstraZeneca vaccine outweigh risks:

Tam says benefits of AstraZeneca vaccine outweigh risks

Politics News

3 months ago
1:53
Canada's Chief Public Health Officer Dr. Theresa Tam says the benefits of the AstraZeneca COVID-19 vaccine outweigh the rare risks. 1:53

Three of the seven patients in Germany who were recently vaccinated with the AstraZeneca-Oxford shot that had this rare brain blood clot have died.

In its investigative document, the EMA said it would expect to see just 1.35 cases of CVST in the time period it looked at — but instead its researchers saw 12.

Germany and Italy resumed vaccinations with the shot on Friday, but France opted to vaccinate only those over 55 with the AstraZeneca vaccine after discovering three cases of CVST. Denmark, Sweden and Norway decided to hold off on using the vaccine until at least next week, citing the need for more time to investigate.

Findings 'need to be investigated'

"You cannot brush adverse effects under the rug. They always need to be investigated, and I think we have to look at this in a careful and critical manner," said Dr. Isaac Bogoch, an infectious diseases physician and member of Ontario's COVID-19 vaccine task force.

"We don't have all the information yet and we'll learn more about this — and I imagine we'll see some updated guidance on who should get this vaccine and perhaps who shouldn't be getting this vaccine."

Health Canada released a statement on Thursday saying the benefits of the AstraZeneca-Oxford vaccine outweighed the risks.

During a media briefing a day later, Dr. Marc Berthiaume, director of the department's Bureau of Medical Sciences, echoed those remarks but noted officials are "actively monitoring" emerging research on the AstraZeneca-Oxford vaccine and are in contact with European counterparts.

"Health Canada is aware that researchers in Europe have indicated that they have identified a possible mechanism for the rare events observed in AstraZeneca COVID-19 vaccine recipients," a followup email statement to CBC News on Saturday read.

"Health Canada will continue to monitor these developments closely and will incorporate guidance to health professionals in ongoing communications, where appropriate."

Researchers in Norway reported identifying the mechanism early Friday, saying it was due to a "powerful immune response" following the vaccine.

The AstraZeneca vaccine is prepared at the local vaccination centre in Hagen, Germany. Germany and Italy resumed vaccinations with the shot on Friday, the day after the European Medicines Agency found there was no increased risk of blood clots from the vaccine. (Kai Pfaffenbach/Reuters)

German researchers corroborated that finding, adding they had found a typical intravenous immunoglobulin treatment that can be offered to patients in hospitals if this rare type of blood clot occurs, but they said it wouldn't work as a preventive measure.

"Of course you can't completely undo a complication," Dr. Andreas Greinacher, a professor of transfusion medicine at the Greifswald University Clinic, said during a news conference in Germany.

"But at least now we can offer the right treatment to be able to help as quickly as possible and as efficiently as possible."

Potential blood clot link could alter rollout in Canada

The potential link could have massive implications on the rollout of the vaccine in Canada and other countries, after use of the shot was halted in parts of Europe over safety concerns in connection with the adverse events last week.

Health officials now face the unenviable task of either adjusting the rollout or trying to restore confidence in the shot, at a time when a variant-driven third wave is unfolding and many vulnerable Canadians are vastly underprotected from COVID-19.

The National Advisory Committee on Immunization (NACI) recommended earlier this month that Canadians over 65 not receive the shot, despite emerging evidence from around the world demonstrating its ability to prevent severe COVID-19 in older adults.

But that guidance changed on Tuesday after more real-world data on the vaccine's effectiveness was reviewed by NACI, and CBC News broke the story revealing documents on the federal government's plans to allow those 65 and older to receive it.

Experts say that while the guidelines for the vaccine could further change and it may not be recommended for certain age groups in the future, the protection against COVID-19 provided by the AstraZeneca-Oxford shot vastly outweighs the risk of rare adverse events.

That being said, we still don't have all of the answers, and Canadians need to be aware of potential risks moving forward — however small they may be.

Medical experts in Canada divided over findings

Dr. Michael Hill, a professor of neuroscience at the University of Calgary's Cumming School of Medicine, said on Friday that while the finding out of Europe is interesting, he remains skeptical of the potential link.

"For now, the case prevalence is such that it could still be a coincidence," he said. "We just do not know."

Hill said that as new data emerges, new questions will arise until there is enough evidence to meet the criteria to either confirm or deny a causal link to the vaccine.

WATCH | WHO finds AstraZeneca vaccine safe and effective:

WHO finds AstraZeneca vaccine safe and effective

Health

3 months ago
1:09
The World Organization's advisory committee on vaccine saftey says the AstraZeneca COVID-19 vaccine's benefits outweigh the risks and the shot saves lives. 1:09

"The data will evolve further over time," he said. "Meanwhile, a very large set of randomized trial data has shown no increased major adverse events with the AstraZeneca vaccine compared to placebo."

Dr. David Fisman, an epidemiologist at the University of Toronto's Dalla Lana School of Public Health, said German data offered a "compelling picture" that the rare blood clots were potentially linked to the vaccine in rare cases.

"I find myself in disagreement with Health Canada's guidance on the use of AstraZeneca," Fisman said.

"I do think that the use of this vaccine should be suspended in Canada until we have more data. At a minimum, I do not think it should be used in women aged 20 to 50 until we know more."

Fisman said while the messaging around the AstraZeneca shot would be "challenging," the continued use of the vaccine in the face of the issue that he believes will become "more apparent" as surveillance increases could erode trust in COVID-19 vaccines.

"I appreciate that this is a sunk cost and is politically difficult. I appreciate that vaccines have become a political football," he said.

"That said, I think suspension of use of [AstraZeneca-Oxford] will create short-term discomfort but is the right thing to do in the longer term."

In a statement on Saturday, a day after the new findings were released, Health Canada said in a statement that it 'will continue to monitor these developments closely and will incorporate guidance to health professionals in ongoing communications, where appropriate.' (Hannibal Hanschke/Reuters)

Dr. David Juurlink, head of clinical pharmacology at Sunnybrook Health Sciences Centre in Toronto, said the rare events may signal a causal link with the vaccine but need to be put in context even if they are confirmed.

"If people are foregoing vaccination — AstraZeneca or otherwise — because of fear of some infinitesimally rare adverse effect, they run the risk of dying," he said.

"I think it's probably fair to make the claim that the countries in Europe that went against the advice of their regulator and suspended the use — that may cost some of their citizens in those countries their lives."


To read the entire Second Opinion newsletter every Saturday morning, subscribe by clicking here.

ABOUT THE AUTHOR

Adam Miller

Senior Writer

Adam Miller is a senior health writer with CBC News. He's covered health, politics and breaking news extensively in Canada, in addition to several years reporting on news and current affairs throughout Asia.

Add some “good” to your morning and evening.

A variety of newsletters you'll love, delivered straight to you.

Sign up now

Comments

To encourage thoughtful and respectful conversations, first and last names will appear with each submission to CBC/Radio-Canada's online communities (except in children and youth-oriented communities). Pseudonyms will no longer be permitted.

By submitting a comment, you accept that CBC has the right to reproduce and publish that comment in whole or in part, in any manner CBC chooses. Please note that CBC does not endorse the opinions expressed in comments. Comments on this story are moderated according to our Submission Guidelines. Comments are welcome while open. We reserve the right to close comments at any time.

Become a CBC Member

Join the conversationCreate account

Already have an account?

now