Cause for concern with AstraZeneca vaccine?
Canada to decide soon, despite some countries’ putting brakes on shots
Canadian regulators are believed to be on the verge of approving a third COVID-19 vaccine.
But recent developments have raised some questions about the dose made by the University of Oxford in partnership with Swedish-British pharmaceutical company AstraZeneca.
The shot is currently approved in jurisdictions around the world, including the United Kingdom, Morocco and Mexico. Last month, after it was greenlit by the European regulator, with whom Canada has been sharing information, Health Canada said it expected to make its own decision in the coming days.
But the Swiss regulator hit the brakes last week, saying available data was “not yet sufficient.” Then, on Monday, South Africa paused its rollout of the vaccine after a study reportedly showed it offered less protection against the COVID-19 variant first identified in that country.
So should Canadians be concerned?
Not necessarily, says Alan Bernstein, president and CEO of global research organization CIFAR and a member of Canada’s vaccine task force.
The rise of virus variants have made the business of testing and evaluating vaccines even harder. He said Pfizer and Moderna both did their trials in summer and fall — before, it’s believed, the COVID-19 variants had major traction.
The newer crop of vaccines likely encountered the variants in trials and now regulators are being forced to make decisions based on which versions of the virus are circulating locally.
“The results are a bit more complicated, and they’re a bit more difficult to sift through,” Bernstein said. “And a lot depends on what country we’re talking about.”
The variant that began in South Africa is still scarce in Canada, he points out. Meanwhile, the United Kingdom, where health officials have been injecting AstraZeneca doses into arms for weeks, is acting as a “living lab” for how the vaccine works in the real world, which will provide more information to regulators.
In addition, the AstraZeneca trials have different end points, Bernstein said. Meaning, they set out to answer slightly different questions. The trials of the first mRNA vaccines — Pfizer and Moderna — were focused on whether the vaccines prevented disease. The AstraZeneca trials delved into whether its dose prevented serious disease or hospitalization.
Depending on how you look at it, AstraZeneca arguably set the bar a bit higher, he said, which means the results take a bit longer to untangle.
Leaders from multiple western governments defended the vaccine Monday, with some officials noting that the trial in South Africa was relatively small and not yet reviewed by other scientists.
“We think that both the vaccines that we’re currently using are effective in, as I say, in stopping serious disease and death,” British Prime Minister Boris Johnson told reporters, according to Reuters. Britain is also using Pfizer’s vaccine.
Sarah Gilbert, lead researcher for the Oxford team, told the BBC on Sunday, “We have a version with the South African spike sequence in the works.”
“It looks very likely that we can have a new version ready to use in the autumn,” she added.
The decision on whether or not to authorize the vaccine here ultimately rests with Health Canada, which began its process back in October. The regulator has made clear its commitment to an “independent and thorough scientific review” of all vaccines.
There’s no question an approval would help ease supply woes. If AstraZeneca were to be authorized, federal officials said last week, we could see as many as 1.9 million doses in the country by June.
Long one of the global frontrunners in the vaccine race, the AstraZeneca shot is expected to be cheaper and easier to store than Canada’s current two options.
That makes transportation less problematic, not just for remote communities here, but for countries around the world, for which it could be a gamechanger.
Like the two vaccines currently approved here, the AstraZeneca is a two-dose regime, given at least 28 days apart. But unlike Pfizer and Moderna, it doesn’t depend on the muchtalked about mRNA technology. Instead, it uses a virus normally found in chimps to sneak a bit of the coronavirus’s genetic code into your body, mimicking an infection.
Some regulators have questioned the vaccine’s effectiveness in older adults. The European regulator has said there’s not a lot of data for older adults but that protection is expected; whereas multiple countries, including Germany, Sweden and Norway, are advising against giving the dose to those over 65.
Meanwhile, an early mistake saw some trial volunteers receive the wrong dose — a stumble some say has muddied understanding of the AstraZeneca vaccine’s overall efficacy.
Back in November, the dose’s initial efficacy was reported to be about 70 per cent, though ranging from about 63 per cent on the low end to as high as 90 per cent. An analysis in a journal called the Lancet showed similar results in early December.
AstraZeneca explained the gap in a news release, in which it revealed it had actually tried out two different doses in one of its trials — and that had delivered two different results.
It turns out that most of the volunteers had received two full doses of vaccines a month apart, as planned. The vaccine for them was 62 per cent effective.
But a second, smaller group got only a half dose in their first shot — then a full dose a month later. For that second group, the vaccine was more effective, showing that 90 per cent efficacy rate.
So that overall 70 per cent number was the result of averaging the two groups, which drew criticism from some experts. Immunization expert and professor David Salisbury told the BBC at the time, “You’ve taken two studies for which different doses were used and come up with a composite that doesn't represent either of the doses. I think many people are having trouble with that.”
This has meant regulators have had a choice to make: Do they go with the two-full-dose regime, which has been tested more rigorously? Or go for the half-dose, full-dose option, which might be more effective.
Both the European Union and Britain opted for two full doses, which is about 60 per cent effective but has more data to back it up.