The more than two million Canadians who received the AstraZeneca-Oxford COVID-19 vaccine made the right choice and should not regret their decision, health experts say, despite the fact that some provinces are pausing rollout of the vaccine over concerns about the risk of rare blood clots.
In fact, Dr. David Naylor, co-chair of the national COVID-19 Immunity Task Force, thanked those who received the AstraZeneca vaccine, saying their actions protected them and others around them.
He noted that when AstraZeneca first came into use, several provinces were in the grips of an intensifying third wave of COVID-19.
"The risks were obvious, with scores of Canadians dying every week and many more hospitalized, including those with illness severe enough to require intensive care and mechanical ventilation," he said in an email.
"It made very good sense in those circumstances to follow public health advice about taking the first vaccine on offer."
Dr. Zain Chagla, an infectious diseases physician at St. Joseph's Healthcare Hamilton, agrees. He said that four weeks ago, Ontario was seeing skyrocketing cases, and the future path of the pandemic was uncertain.
"It's easy to forget how bad things really looked and how much health care was, you know, on the brink of collapsing," he said.
"It would be stupid not to take a vaccine at that point to at least protect yourself from what was coming, in case we dealt with the worst-case scenario."
WATCH | Reassurance for those who received AstraZeneca vaccine:
Ontario's outbreak response co-ordinator, Dr. Dirk Huyer, told CBC News getting the AstraZeneca vaccine in that period "was so much the right move."
"It helped to provide not only individual protection but also broader protection to help reduce the burden of illness in Ontario."
According to Chagla, "People should feel good they got the shot."
Evolving data on risks
While some provinces have announced they will stop administering AstraZeneca due to supply issues, Ontario, Quebec and Nova Scotia are citing the small but potentially dangerous risk of vaccine-induced immune thrombotic thrombocytopenia (VITT), a blood-clotting condition that can cause fatal bleeding.
The Public Health Agency of Canada said there have been 18 confirmed cases of VITT after vaccinations of AstraZeneca, including three deaths in Quebec, Alberta and New Brunswick, with 10 other possible cases under investigation.
Initially, the National Advisory Committee on Immunization projected the VITT risk at one in 250,000. That was recently amended to one in 100,000.
The Ontario Science Table now estimates it at one in 55,000, but that number is a moving target, with new data being released from countries around the world daily.
In the United Kingdom, where the majority of people have been inoculated with AstraZeneca, there have been 242 reports of VITT out of 28.5 million doses given. There have been 49 deaths.
Dr. Alyson Kelvin, a virologist at Dalhousie University, said the AstraZeneca vaccine was needed to help achieve community immunity in Canada, and seemed like a great choice.
She said while there's a high amount of protection in people who received AstraZeneca, new evidence suggests there are safer options.
Naylor said that with the immunization effort in Canada proceeding faster and a flood of mRNA vaccines available that so far do not have any major side-effects, it is reasonable for vaccine campaigns in some provinces to switch over to the Pfizer and Moderna products.
Some people concerned they were 'duped'
Dr. James Douketis, who is president of Thrombosis Canada and specializes in the study of blood and blood clots, said he has been fielding questions from people asking if they "were duped" at the time into getting the AstraZeneca vaccine.
"I say to them, 'No, you weren't. At that time you were doing the right thing for yourself, your family and your community. No question at all."
But months later, with more mRNA vaccines available, more people vaccinated, hospitalization rates somewhat steady, the situation is different, Douketis said.
"Why subject people to a risk, however small it is, when we've got some options or we've got some flexibility?"
For those who had their AstraZeneca shot more than a month ago, the window of VITT risk has closed, Naylor said.
For people who have had a shot recently, Naylor stressed that the serious clotting side-effect is rare, and current estimates are that 99.998 per cent of people who get an Astra Zeneca jab will not be affected.
Still, he said, people should pay attention to any potential side-effects. Those include:
Persistent and severe headache.
Difficulty moving part of your body.
Problems with your vision, including blurry or double vision.
Shortness of breath.
Severe chest, back or abdominal pain.
Swelling or colour change in an arm or leg.
What about the 2nd shot?
On Wednesday, the federal government confirmed that Canada will receive 655,000 more doses of AstraZeneca by next week. For Canadians anxious about receiving a second dose of AstraZeneca, Naylor said early data from the United Kingdom suggests the risk of VITT with the booster shot is an order of magnitude lower than with the first dose.
"This is very reassuring, but we should wait for definitive tallies," he said.
Meanwhile, researchers are studying mix-and-match immunization with Pfizer and AstraZeneca in different orders and at different intervals.
If these strategies are safe and effective, as seems likely, then the option of a follow-up mRNA vaccine will come into play, Naylor said.
Early results from one U.K.study have shown that mixing different types of COVID-19 vaccines for two doses can increase the chance of someone having mild or moderate reactions like fatigue, headache or a fever.
"One way or another," Naylor said, "it's expected that boosters will be available to everyone who has had an AstraZeneca vaccine."