No biological explanation for linking AstraZeneca vaccine to blood clots: Sharma
OTTAWA – Health Canada’s chief medical adviser says there is no scientific explanation suggesting a link between the Oxford-AstraZeneca COVID-19 vaccine and blood clots.
Dr Supriya Sharma says Health Canada has a “really low threshold” for adverse events that could trigger a pause in vaccine use and would not hesitate to do so if something warranted.
But she says the science isn’t there to suggest the Oxford-AstraZeneca vaccine could be the reason some patients in Europe developed blood clots after receiving it.
“There isn’t a good biological explanation as to why a vaccine like this, injected into a muscle, would cause this kind of adverse event,” Sharma said in an interview with The Canadian Press.
Denmark, Iceland, Norway and Bulgaria are among a dozen European countries that suspended use of the Oxford-AstraZeneca vaccine this week – either entirely or specific batches of it – following that some patients develop blood clots afterwards. None of them said there was evidence of a link, but the hiatus was due to an abundance of caution while awaiting a review.
Austria stopped using doses of a vaccine batch earlier this week after two reports of blood clots, but experts concluded that neither was related to the vaccine. Austrian Chancellor Sebastian Kurz said on Friday he would be ready to get the vaccine himself to show how much he trusted him.
Many other countries, including Germany, France, Poland, Nigeria, the UK and Canada, are sticking to AstraZeneca injections, citing the lack of any evidence showing a link.
The vaccine has been cleared in 74 countries and by the World Health Organization, and 16 million doses have been injected in the UK and Europe alone.
Canada approved it on February 26 and the first 500,000 doses were distributed to the provinces this week, just as concerns about blood clots began to become public.
Lucilia Pato, who received her first dose on Friday morning at Junction Chemist in western Toronto, said news that some European countries had stopped using AstraZeneca’s vaccine for the time being had initially given her a break.
“I was (worried) when I heard about it yesterday, but this morning I heard some positive things about it, so you know what, I was ready to give it a go,” he said. she declared.
The European Medicines Agency, which regulates new medicines for the European Union, said in a statement Thursday that it was not suspending its authorization for the AstraZeneca vaccine.
“There is currently no indication that the vaccination caused these conditions, which are not listed as side effects with this vaccine,” the EMA said.
Sharma said reviews of adverse events are normal after a new drug or vaccine is released.
“Once vaccines are used in nature, and by millions of people, these things will present themselves,” she said. “So we’re already in a system where we expect things to pop up and that’s why we have these vigilance systems to be able to detect them.”
Sharma said the first question to always ask is whether there is anything scientific to explain a link between an adverse event and a vaccine.
“And when we look at the AstraZeneca vaccine, as an example, there isn’t one in this case,” she said.
She said regulators are also asking if the number of patients experiencing the effect is higher than what might normally be seen in the population and if there is another factor common to all patients with the problem.
The answer to every question here is also no.
Finally, Sharma said regulators would consider the possibility of a manufacturing error with a particular batch. While there is no evidence for this in Europe either, Canada’s doses of the Oxford-AstraZeneca vaccine are also not from the same source as those in Europe.
The doses of the vaccine currently in use in Canada were produced at the Serum Institute of India.
Canada has authorized four separate COVID-19 vaccines and nearly 2.8 million doses have been injected.
Sharma has said so far that no “adverse event” in Canada has been unexpected or more frequent than expected.
She said Health Canada would respond soon to the safety concerns. The people who make these decisions know that it is not just Canadians as a whole, but themselves and their families who will receive the same vaccines.
“These are our fathers, brothers, sisters, mothers,” she said. “We want to make sure we’re doing our best for them as well.”
This report by The Canadian Press was first published on March 12, 2021.
–With files from Paola Loriggio in Toronto