OTTAWA -- The chair of the National Advisory Committee on Immunization says people who already got the Oxford-AstraZeneca vaccine should not feel they made a bad choice.

Dr. Caroline Quach and the other 15 members of NACI were accused of sowing seeds of confusion and vaccine hesitancy when they recommended for a second time that Canadians who aren't at high risk from COVID-19 may want to wait to get immunized until a dose of Pfizer-BioNtech or Moderna is available.

Those two vaccines, which use mRNA technology and haven't been linked in any way to blood clots, are the "preferred" vaccines, they said, leading some medical experts to worry NACI was grading the vaccines and Canadians would wonder if that means AstraZeneca is substandard and should therefore be avoided.

Some of the 1.7 million Canadians who had been vaccinated with it already questioned whether they should have waited instead.

Quach said people who took AstraZeneca did not get a "second-best shot."

"The recommendation is not a retrospective one," said Quach. "That means that everyone who has received the AstraZeneca vaccine has been protected against COVID-19."

Quach said a single dose of AstraZeneca has proven to be as good at preventing hospitalizations or deaths from COVID-19 as a single dose of Pfizer or Moderna. That includes against both the original SARS-CoV-2 virus that causes COVID-19, and the B.1.1.7 variant of it.

That variant is the dominant one in Canada.

"People who did get their AstraZeneca vaccine, mainly when COVID-19 was being transmitted in their community, actually did the right thing," she wrote. "They protected themselves and their families against COVID-19 complications."

They also got it at a time when it wasn't entirely clear when they might be able to get a dose of Pfizer or Moderna. Most people going forward won't have to choose between AstraZeneca now or an mRNA later, because more than 80 per cent of the doses coming to Canada in the next two months are mRNA.

Almost all the 2.3 million doses of AstraZeneca already delivered have been used, and only 655,000 doses are scheduled to arrive this month. Another million are expected in June.


That does not hold for people who live in places with high infection rates, or who are at high risk of serious illness or death from COVID-19.

"If your risk of COVID is moderate to high, get the first vaccine available now," she said.

"If not, then one needs to balance out the risk of COVID complications against the risk of VITT that, although rare, does exist and may lead to severe complications."

Dr. Fahad Razak, a general internist who treats COVID-19 patients at St. Michael's Hospital in Toronto, said NACI's communication of its advice was more problematic than the advice itself.

He said the doctors, nurses and other vaccine experts on NACI are "incredibly smart and well-meaning" but that they, like he and other scientists and medical experts, aren't experts in communications.

"I think the challenge that you saw this week is in the messaging, of how to talk about a very serious but rare side effect, and how to say that in a way that doesn't lead to people worrying about vaccines in general," he said.


Canada has confirmed 12 cases of VITT -- vaccine-induced thrombotic thrombocytopenia. Three women have died.

The blood clot risk did not surface during clinical trials but was picked up in Europe after widespread use of AstraZeneca began. Health regulators in Canada, the United Kingdom and Europe rapidly investigated and concluded the risk is somewhere between one case in every 100,000 doses and one in 250,000.

But they said the risks of COVID-19 are much greater, VITT is generally treatable if it is diagnosed on time, and therefore the benefits of getting vaccinated still outweigh the risks.
