Authorities in Canada are seeking to reassure the public that the AstraZeneca-Oxford vaccine is safe, after several more European countries suspended the vaccine over reports of blood clots.
The situation has resulted in confusion and concern among the public and delays at vaccination sites in Montreal where health-care workers have been trying to explain the merits of the vaccine to those who are set to receive it.
Here is a look at what we know and what we don't.
Authorities in Canada say vaccine is safe
Prime Minister Justin Trudeau said Monday the AstraZeneca-Oxford is safe and Canadians should have no concerns about receiving it.
"Health Canada and our experts have spent an awful lot of time making sure every vaccine approved in Canada is both safe and effective," Trudeau said.
"The best vaccine for you to take is the very first one that is offered to you. That's how we get through this as quickly as possible and as safely as possible."
Trudeau said regulators are "following what has been happening with a specific batch used in Europe." He said none of the AstraZeneca doses deployed in Canada have come from that batch.
European countries suspend vaccine out of caution
Nearly a dozen countries including Germany, France and Italy have all temporarily suspended their use of AstraZeneca's coronavirus vaccine after reports last week that some people in Denmark and Norway who got a dose developed blood clots, even though there's no evidence that the shot was responsible.
Authorities in the Netherlands — like those elsewhere — said their suspension of the AstraZeneca vaccine was strictly precautionary.
"We must always err on the side of caution, which is why it is sensible to press the pause button now as a precaution,'' said Hugo de Jonge, the Dutch health minister.
In response to the suspensions of its vaccine, AstraZeneca said it had carefully reviewed the data on 17 million people who received doses across Europe and found there were 37 cases where people developed blood clots. It said there was "no evidence of an increased risk'' of blood clots in any age group or gender in any country.
"This is much lower than would be expected to occur naturally in a general population of this size and is similar across other licensed COVID-19 vaccines,'' the company said.
No evidence vaccine leads to blood clots
In a statement last week, Health Canada said there is no indication the vaccine has had any adverse effects on people in Canada.
"Health Canada authorized the vaccine based on a thorough, independent review of the evidence and determined that it meets Canada's stringent safety, efficacy and quality requirements," the department said on March 11.
In Britain, where 11 million doses of the AstraZeneca vaccine have been administered — which is more than any other country — there have been reports of about 11 people developing blood clots after getting a shot. None were proven to have been caused by the vaccine.
Experts back that claim
Experts have pointed out that since vaccination campaigns started by giving doses to the most vulnerable people, those now being immunized are more likely to already have health problems. They say that could make it difficult to determine whether a vaccine shot is responsible.
"Remember that millions of people have gotten the AstraZeneca vaccine in Europe," said Dr. Christopher Labos, a Montreal cardiologist with a degree in epidemiology.
"So, when you look at the number of people who have gotten blood clots versus the number of people who have been vaccinated, well that's just the baseline risk."
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Labos said some people would have gotten blood clots anyway, even without getting the vaccine, especially those who are older with pre-existing medical conditions.
"One of the great ironies is that COVID does seem to increase your risk of getting blood clots, so even if there was a small theoretical risk with the vaccine, it would probably be lower than the risk of getting COVID," he said.
Benoit Barbeau, a virologist in the department of biological sciences at the Université du Québec à Montréal, said the Quebec government must make it clear the vaccine remains safe.
He said people were also apprehensive and concerned about the Pfizer-BioNTech vaccine until those concerns were debunked.
"It has been studied and in several clinically based trials and there are millions of doses out there which have been distributed, and there's been very few cases of these blood clot problems. So the issue remains a very low number, and I think that needs to be taken into consideration."
CBC News learned on Monday that Canada will change its guidelines on the AstraZeneca-Oxford vaccine to recommend it be given to those over 65.
The National Advisory Committee on Immunization (NACI) had previously recommended 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.
Quebec had already decided to administer the AstraZeneca-Oxford vaccine to seniors.
The province's vaccine expert committee said the vaccine is safe and "provides more flexibility in immunization efforts, especially for priority groups aged 70 to 79.''
In Quebec, it is primarily being administered to those in home care, but also is being used in some vaccination clinics, while Pfizer-BioNtech's is being administered in clinics and Moderna's in pharmacies.
Some Quebecers turning down the shot
As the situation unfolds, some residents are refusing to get their shot when they learn they are getting the AstraZeneca-Oxford vaccine.
As of March 11, Quebec had received 113,000 doses of the Covishield branded version of the AstraZeneca-Oxford vaccine (compared with 606,000 doses of Pfizer-BioNTech and 133,000 doses of Moderna).
In the CIUSSS du Centre-Ouest-de-l'Île-de-Montréal, roughly 12 per cent of people refused the AstraZeneca-Oxford vaccine, while in Nord-de-l'Île-de-Montréal roughly eight per cent of people who signed up refused, according to authorities.
Quebec Health Minister Christian Dubé took to Twitter on Sunday to say the vaccine is safe and effective. He also thanked health-care workers at vaccination clinics for taking the time to explain the benefits.
"The vaccine is the solution, no matter which one," he said.
The AstraZeneca-Oxford vaccine had already been under scrutiny for questions about its efficacy rate. It has an efficacy rate of 62 per cent, compared to around 95 per cent for Pfizer-BioNtech and Moderna.
Despite different efficacies, trials have shown that those who did become infected after getting vaccinated experienced only mild illness, experts say.
Of the thousands of participants in trials for the vaccines, not a single person who received a shot died or was hospitalized from COVID-19, Dr. Sumon Chakrabarti, an infectious disease specialist in Mississauga, Ont., recently told The Canadian Press.