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Prime Minister Justin Trudeau holds a press conference in Ottawa on April 27, 2021.Sean Kilpatrick/The Canadian Press

Prime Minister Justin Trudeau reiterated that Canadians should get the first COVID-19 vaccine they can, contradicting the recommendation from an independent vaccine advisory group that people who are at lower risk of contracting the novel coronavirus should wait for a preferred shot.

Mr. Trudeau made his comments the day after the National Advisory Committee on Immunization (NACI) upheld its position that waiting for an mRNA vaccine, like those from Pfizer-BioNTech and Moderna, is preferable to receiving a viral vector vaccine, from Johnson & Johnson and AstraZeneca, when personal risk of contracting COVID-19 is lower.

NACI’s Monday advice was criticized by physicians and scientists who said it created a hierarchy of vaccines and unnecessarily stoked distrust of a vaccine that played a leading role in subsiding Britain’s third wave.

Mr. Trudeau said his advice “has not changed” and he told the House of Commons his message to Canadians is, “The most important thing is to get vaccinated with the first vaccine offered to them. It is how we get through this.”

At issue is how NACI is communicating the risk of a very rare blood-clot syndrome coupled with low platelets, which has been linked to the AstraZeneca and Johnson & Johnson vaccines, but not the mRNA shots.

Eight cases of the syndrome, called vaccine-induced immune thrombotic thrombocytopenia, or VITT, have been reported to Health Canada. One woman in Quebec died.

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On Monday, NACI said “it continues to preferentially recommend authorized mRNA COVID-19 vaccines.”

NACI said Canadians who consider themselves at low risk from the coronavirus – such as healthy people who can work from home and who live in places with relatively few cases – would be better off to wait for the mRNA vaccines. The advice attempts to balance the risk of the blood clots against the risk of getting seriously ill with COVID-19; it was also given by the group on April 23. However, it received much more attention on Monday, particularly after by comments made by NACI’s chair Caroline Quach-Thanh.

“If, for instance, my sister was to get the AstraZeneca vaccine and die of a thrombosis, when I know that it could have been prevented and that she is not in a high-risk area, I’m not sure I could live with it,” Dr. Quach-Thanh told CTV News.

The comment and NACI’s advice was met with a social-media firestorm. Experts called it a failure to communicate that did not properly contextualize individual risk with the broader community benefit of the vaccines. The advisory group on Tuesday defended its guidance, and some experts sympathized with the challenges it faces in responding to quickly changing evidence and explaining complex and nuanced information to the public.

Dr. Quach-Thanh said the example she offered to CTV was a poor one. But she stood by the committee’s recommendation, which hinges on the fact that Canada is receiving vastly more mRNA vaccines than viral vector vaccines.

“What we’ve asked people to do is to do an individual risk assessment based on what’s happening around [them], based on what [they] do,” said Dr. Quach-Thanh, who is an infectious disease specialist and professor at the University of Montreal.

Though data vary by country, the risk of blood clots from the AstraZeneca vaccine is estimated to be somewhere in the range of 1-in-100,000. In April, Health Canada said the shot is “very low risk” for an adverse reaction while the risk of COVID-19 is moderate to high in much of the country. Health Canada is holding back use of the Johnson & Johnson vaccine, pending an unrelated quality assurance review.

Dr. Quach-Thanh agreed with the low risk assessment but said that doesn’t mean NACI can “put that under the carpet.”

She said the group could do more harm to public confidence by not being transparent about where it stands on the evolving science around the vaccines.

Timothy Caulfield, a professor of health law and science policy at the University of Alberta, said NACI has a “tough job.” But he said the advisory panel focuses largely on individual risk and “underplays the benefit to the public – that is, achieving herd immunity and reducing community spread.”

“I view getting a vaccine as an altruistic act. Something you do for your community,” he said. “I also think the rarity of these risks needs to be put in context. Everything in life has risks.”

Alberta currently has the highest infection rates in North America and the Canadian Armed Forces are providing back-up in Toronto’s hospitals. Through a combination of lockdowns and a mass vaccination campaign that started months before Canada’s, Britain has kept a lid on cases for almost a month. In Britain, 59 per cent of administered vaccines were from AstraZeneca, according to data up to April 21.

As far back as March 1, NACI has said that mRNA vaccines are a preferred option for high-risk groups who were prioritized for early vaccination. At the time, though, the distinction was purely academic: No viral vector vaccines had been shipped to Canada; mRNA vaccines were scarce; and experts were warning of a third wave.

Now the committee’s detailed balancing act of the risks of the viral vector vaccines and COVID-19 are clashing with a straightforward public-health message that all approved vaccines are safe and people should get the first one they’re offered.

In part, the different messages and the ensuing confusion has to do with the way NACI’s role differs from that of regulators at Health Canada. Made up of independent, unpaid experts, the committee convenes to provide non-binding advice on how vaccines should be prioritized. And unlike regulators who approve vaccines separately based on safety and efficacy data, NACI is also in the position of having to compare the different vaccines and vote on who should get them.

Canada’s Chief Public Health Officer Theresa Tam came to NACI’s defence, noting that the science is evolving. But she also underscored the value of the AstraZeneca shot.

“The AstraZeneca vaccine, deployed in the middle of a third wave, has saved lives and prevented serious illnesses,” Dr. Tam said.

Menaka Pai, a hematologist and thrombosis medicine physician at Hamilton Health Sciences, said NACI’s recommendations are “correct, the content of what they’re saying, scientifically. It made sense to me.” But she said the information was poorly communicated to people, leaving them with buyer’s remorse and confused if they made the right call to get the AstraZeneca shot.

“That really must feel like a betrayal to people. I feel so bad about that,” she said.

Dr. Pai, whose specialty is treating blood clots, said NACI had little choice but to acknowledge the small but serious risk of the rare clotting syndrome linked to the AstraZeneca and Johnston & Johnson vaccines, then balance it against the risk of severe outcomes from COVID-19.

Soon after the AstraZeneca vaccine became available to Canadians in March, emerging blood-clot cases in Europe began to colour public perception. Andrew Morris, an infectious disease physician at Toronto’s University Health Network, said the new information complicated the public-health message.

“To me, it was a slam dunk, three or four weeks ago: Any vaccine you can get you should probably take unless you can be absolutely certain that you’re not seeing another human,” Dr. Morris said. “But we’re in a different situation right now.”

Vaccine surveillance systems in Europe, Canada and the United States have identified more cases of the clotting syndrome with low platelets after the AstraZeneca and Johnson & Johnson vaccines, meaning the risk, while still small, is not as infinitesimal as first thought. And at the same time a deluge of Pfizer and Moderna vaccines will arrive in Canada this month.

“It’s really important that that communication includes that it’s a different context,” he said. “It’s been very, very difficult for the public to absorb all this because the messaging really has not been clear.”

Health columnist André Picard outlines how kids could be back in classrooms in the fall, starting with getting all adults vaccinated by Canada Day, followed by a program of vaccinating children with an approved reduced dose ahead of school resuming in September.

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