Only 1.5% of Canadians show COVID immunity
‘Accelerated vaccination is an urgent priority,’ task force head tells MPs
OTTAWA—Canadians are still highly vulnerable to COVID-19, with antibody tests showing only 1.5 per cent of the national population has developed immunity after being infected by the coronavirus.
However, a separate study shows that protective immunity for those who’ve had COVID-19 lasts at least eight months.
Dr. Timothy Evans, executive director of the COVID-19 immunity task force, told a federal health committee Monday, “We are a long way from herd immunity.” And so, he said, “accelerated vaccination is an urgent priority.”
The task force, working with Canadian Blood Services, funded antibody or seroprevalence tests that sampled 33,860 blood donations at blood donor centres across the country during the first and second waves of the pandemic.
In May and June last year, samples showed the level of population immunity was “extremely low,” Evans said, at below one per cent. In November, the level had almost doubled but remained low at just over 1.56 per cent nationally.
The picture varies across the country, with just 0.77 per cent of Ontario residents showing antibodies while more than 8.5 per cent immunity was detected in the Prairies.
Dr. Catherine Hankins, cochair of the task force, said in an interview the doubling of the seroprevalence number nationally “is a concern.”
“I don’t consider it to be good news because it does show the vast majority of people are still susceptible to this. And, if we start to get variants start circulating … we’re still sitting ducks for community transmission.”
“This is a little bit of a wake-up call to Canadians that we’ve got to keep doing what we’re doing,” she said. “We are moving forward on vaccine rollout, but it’s kind of a race against time to get the vaccines out and to stop variants being transmitted. So we’re very highly vulnerable.”
Dr. Isaac Bogoch, an infectious disease specialist with Toronto General Hospital and University of Toronto, delivered the same message to the Commons health committee.
He said most regions of Canada have emerged from peak cases in December and early January and are now seeing a decline or a plateau in new cases because of tight controls.
But Bogoch said, “We still have a long, long way to go. Vaccines are trickling in, but we won’t really be able to really start massive expansion of these programs until the spring.”
Bogoch warned about the threat of spreading new variants. Vaccines have shown to be effective against the variant first found in the U.K., but less so against the variant that first cropped up in South Africa — and has now been reported in Ontario.
“We have to respect this, we have to take it seriously,” Bogoch said. “And we need to drill down on our current control efforts, until vaccine rollout is more widespread.”
For those Canadians who have been infected by the virus, there is some good news in what research has found about how long immunity might last.
The COVID-19 immunity task force reported a separate study by Dr. Daniel Kaufmann and Dr. Andres Finzi, researchers from Université de Montréal, who along with researchers at New York University looked at that question.
It found that, although antibodies eventually decay over time, the cells that produce antibodies last for up to eight months.
Those cells are able to “remember the virus” and “are capable of fighting potential new infections faster and better than the original cells” — results that were detected in all of the recovered COVID-19 patients that the study looked at, according to the task force’s summary of the study, which was pre-printed last week.
Hankins said “we don’t fully understand immunity,” but researchers are moving to use a stronger assay or test that picks up both infection-acquired immunity and vaccine-induced immunity — which will be important to understand issues around vaccine efficacy and herd immunity.
Hankins said that with variants emerging that make the virus more infectious, Canada’s vaccine uptake will likely need to be closer to 75 or 80 per cent in order to achieve something closer to herd immunity. That’s more than the 60 to 70 per cent vaccine uptake that is ordinarily thought to provide herd immunity with more traditional vaccination campaigns.
Hankins said the seroprevalence testing only revealed part of the current Canadian picture.
Quebec’s blood agency wasn’t involved in the study, so that excludes an entire province that battled a huge wave of COVID-19; the national samples came mostly from a fairly healthy population — young adults over 17 who are likely to be blood donors.
“Older people will not have left their homes to go and donate blood,” she said. “These are volunteers who tend to be healthier and tend to be from an urban population. So it’s missing big parts of the population.”
The testing did reflect higher transmission in Manitoba and Saskatchewan in November, but researchers are puzzled about the lower number shown in Ontario, which, like Quebec, has battled a brutal second wave.
The task force has asked Canadian Blood Services to take another look at Ontario samples.
As well, more studies are underway to test blood samples in specific populations. They include antenatal studies to test pregnant women, in order to determine a fuller picture, she said.
Hankins likened it to putting together a jigsaw puzzle, with the outside frame to be provided by another massive effort to map the spread of the virus. The immunity task force is working with Statistics Canada to distribute 48,000 at-home test kits to Canadians, hoping a madein-Canada pinprick test will show a broader picture.
But the message of the data is clear, Hankins said.
“We have to stay the course,” she said. “Let’s keep this going until we can figure out this variant.”