OTTAWA — Health Canada is devising a warning about a rare possible side-effect of blood clots from the Oxford-AstraZeneca vaccine but is still certain the inoculation is safe and effective against COVID-19.
It is another blow for a vaccine that has now faced everything from a mistake in dosing during early trials, lower efficacy results than its main competitors, confusion about whether it is effective for seniors, and, this week, accusations the company overstated the results from a large trial in the United States.
Health Canada's chief medical adviser, Dr. Supriya Sharma, said at a news conference she is confident the evidence shows the vaccine is safe and effective for adults.
But she says there are concerns that this vaccine is suffering in public confidence.
"We've said this many times before, that even the most effective vaccine only works if people trust it and agree to receive it," she said. "It's like any other reputation — once there's some doubt that creeps into that reputation, it's that much more difficult to gain that back."
Health Canada is adding the blood-clot warning following a similar warning issued by the European Medicines Agency last week after reports 38 people developed blood clots, out of almost 20 million people who were vaccinated.
The warning says the overall risk of blood clots is not heightened by the vaccine but it may cause a very rare blood clot in the brain.
Sharma said symptoms would include sudden, intense or persistent headaches, shortness of breath and pain or tenderness in the legs.
Health Canada authorized the vaccine at the end of February, based on clinical trials in the United Kingdom and Brazil that showed the vaccine was 62 per cent effective against COVID-19 infections and entirely prevented hospitalizations and deaths.
Monday the company reported preliminary results from a trial in the United States that appeared stronger, saying it was 79 per cent effective against infection. That report prompted the independent monitoring board overseeing the trial for the U.S. National Institutes of Health to accuse the company of reporting incomplete data to show a better result.
The board members said their analysis pegged the vaccine's efficacy at between 69 per cent 74 per cent, and said the company's decision to issue a press release with better results erodes public trust.
AstraZeneca said in a statement Monday's preliminary report was accurate with data until Feb. 17, and that its analysis of more recent results are consistent with the preliminary report. It said it plans to issue its report on the updated data within 48 hours.
Sharma said it's not unusual for companies to report preliminary data but said in this case the report came when the company was a lot closer than is typical to knowing what the final data shows. Still, she said, Canada approved the vaccine based on other trials and this doesn't change those trials' findings.
"At this point in time, we, of course, believe that the benefits of the AstraZeneca vaccine continue to outweigh the risks," she said.
Health Canada expects to receive the U.S. trial data within the next few weeks and Sharma said it will be reviewed thoroughly and the findings communicated to Canadians.
Canada has thus far received about 500,000 doses of the Oxford-AstraZeneca vaccine and expects to get 1.5 million more as soon as this week from the United States. The U.S. has a supply of doses it can't use because it hasn't approved them.
Even without those doses Canada's deliveries of more than two million doses of other COVID-19 vaccines from Pfizer-BioNTech and Moderna are the most in a week yet. Though the first of two shipments expected from Moderna has been delayed a day, arriving Wednesday instead of Tuesday.
More than 3.5 million people in Canada have received at least one dose now.
Chief public health officer Dr. Theresa Tam said she knows everyone is tired of the "tricks and turns of this virus" and said there are many reasons to be hopeful, including the faster pace of vaccinations.
Still she warned, variants of concern continue to rise and the number of new COVID-19 cases rose 15 per cent over the last week. In turn, the numbers of people in hospital overall, and those needing intensive care, are creeping upwards.
In the last week an average of 2,100 people were in hospital in Canada being treated for COVID-19 on any given day, including 580 in critical care, compared to 2,040 in hospital and 550 in ICUs a week ago.
Since vaccinations began, COVID-19 infection rates in people over 80 have slowed, said Tam, but younger people, particularly under the age of 40, are seeing higher rates.
Dr. Deena Hinshaw, the chief medical officer of health in Alberta, said 88 per cent of the 48 patients in intensive care in that province are under age 65. Hinshaw said people need to continue to make good decisions to keep the spread of the virus down.
"Now is not the time to abandon the practices that have protected our communities and health care system over the past year," said Hinshaw on Twitter. "Once we hit a growth phase of this virus, our #s will not stand still."
This report by The Canadian Press was first published March 23, 2021.
Mia Rabson, The Canadian Press