Quebec preps for mass antibody tests
The question has stoked curiosity since the daily number of new COVID-19 cases first reached the triple digits in Quebec: what proportion of the population has actually been infected and might now have built up some degree of protection?
Five months into the pandemic in Quebec, the province is about to get its first indication of the infection rate — but the scientific community is cautioning against equating it with lasting immunity.
Quebec’s blood agency, Héma-québec, says it expects to reveal in the coming days the result of a study it began in May to look for COVID-19 antibodies in blood samples from thousands of donors aged 18 to 70. Antibodies are protective proteins made by the body’s immune system in response to an infection, so detecting their presence in blood serum indicates a person has already had the infection.
The study marks the introduction of serologic, or antibody, testing for COVID -19 in the province, and it’s expected to expand from here.
The sample for the Héma-québec study isn’t representative of the population as a whole, but experts say it will provide the first clue of the extent of Quebecers’ exposure to the virus so far.
At the same time, laboratories across the province are preparing for widespread serologic testing for COVID-19 antibodies among targeted groups in the population, such as health-care workers or CHSLD residents, said Dr. Michel Roger, a microbiologist and the scientific director of the Laboratoire de santé publique du Québec.
“We’re waiting for the ‘go’ from Public Health to start the tests,” he said, adding that labs will be able to analyze thousands of tests per day. Quebec’s public health institute will decide what groups or regions it wants to target for antibody testing, he said.
Roger was part of a panel that recently evaluated the performance of serologic kits to be used by Quebec labs to analyze for COVID-19 antibodies.
They’re only waiting now for the capacity of blood testing centres in hospitals and clinics to be boosted so they can handle the extra demand, he said.
At the same time, all of Canada is preparing for antibody testing, said Dr. Catherine Hankins, a professor of public and population health at Mcgill University and co-chair of the leadership group of the Canadian government’s COVID -19 Immunity Task Force. The task force is co-ordinating cross-country antibody testing.
Canadian Blood Services, like Héma-québec, has been analyzing thousands of blood samples for COVID-19 antibodies.
“It’s a snapshot of what’s going on,” Hankins said of the seroprevalence study, which will provide a baseline for more antibody testing down the road. “It will show the proportion of the population in Montreal and Toronto, which have been epicentres in Canada, that have been affected.”
Various countries have carried out antibody testing, and it’s rare for any to have found more than 10 per cent of their populations have antibodies. In certain countries, it’s between one and three per cent.
Don’t hold your breath expecting that antibody testing will lead to “immunity certificates” for those who have recovered from the illness, as some countries talked about early in the pandemic, said Dr. Charu Kaushic, scientific director of the Canadian Institutes of Health Research (CIHR) and a professor of pathology and molecular medicine at Mcmaster University in Hamilton. No one is even talking about herd immunity anymore, because evidence is mounting that COVID-19 antibodies don’t linger for long after recovery.
“Ever since anybody started talking about ‘immunity passports,’ and can we use that to allow people to go back to work and wouldn’t that work wonderfully, most immunologists were cringing,” Kaushic said. “We know that just because you have antibodies, it doesn’t mean that you’re protected.”
Studies are showing that antibody levels start to wane quickly and in many people aren’t detected by available testing after more than two to three months.
“We don’t understand fully,” Kaushic said. “It appears that in some people, the antibody levels start going down very quickly. Is that for everybody? We don’t know yet.
“So far, papers are reporting that the more severe the disease, the higher the antibody levels,” she said. “So that people who are getting the more severe disease from SARS-COV-2 (the virus that causes COVID-19) would get longer-lasting antibodies is not surprising. But the reverse of that is not clear. If you had a mild disease or were asymptomatic, do you not develop antibodies, or do you develop antibodies that disappear in two or three months? Do you develop antibodies that are useless and won’t do anything for protection against the virus? Those things are not clear.”
Preliminary studies show that people with COVID-19 don’t produce a lot of antibodies, the antibodies aren’t very powerful and they don’t last a long time, Roger said. But that has to be validated by further studies, he cautioned.
However, it isn’t the time to despair either, Hankins said.
“Where we’re at right now, and we’re really holding on to this hope, is we don’t have a single proven case of reinfection (of COVID-19) yet,” she said. “So something is helping protect those people who’ve already had it.”
She also noted that researchers have been looking at other coronaviruses, the ones that in the past caused a person to get a cold, and have found that while antibodies wane and people do potentially get reinfected, they get milder symptoms.
“What we don’t know is as the antibodies wane, do we still keep the memory and therefore respond quickly if re-exposed, even if you don’t see antibodies anymore in the blood?” Hankins said. “Are the memory cells still there waiting to mobilize very quickly for whatever comes?”
Researchers also want to know whether other arms of the immune response, such as T cells — specifically CD8 “killer” cells — and Natural Killer Cells, or NK cells, are involved.
One thing is certain: antibody testing won’t replace the nasal swab to screen for active cases of COVID-19, experts say. That’s because the human body only starts producing antibodies days after becoming infected, leaving too much time before testing and isolating an infected person so they don’t spread the virus in the community.
Roger pointed to the findings of a Quebec study, which is consistent with international findings, that 20 to 30 per cent of people developed antibodies seven days after COVID -19 infection. At two weeks, 70 per cent had developed antibodies. And at three weeks after infection, 90 per cent had antibodies.
So to locate active cases, there’s no getting around a swab test that can pick up the virus early in an infected patient.
For now, the purpose of antibody testing will be strictly to measure the prevalence of COVID-19 in the population, Roger said — in other words, who has already had it. Antibody testing will also assist research on COVID -19, he said.
Determining seroprevalence, as it’s called, will help public health authorities decide strategies, Roger said. For example, the authorities might decide they need to ramp up swab testing to diagnose active COVID-19 cases in a particular region of the province if the antibody testing reveals the region had greater exposure to COVID-19 than the number of confirmed cases reveals so far.
The key to slowing the transmission of COVID-19 continues to be rapid testing to find infected people, isolating them and using contact tracing to warn and isolate the people who were in close contact with the infected person, Kaushic said. “It’s not just here,” she said. “It’s the strategy around the globe.”
The ongoing pertinence of rapid diagnosis is being driven home now as Quebec sees clusters of COVID-19 outbreaks, Hankins said.
“They’re like little tiny fires,” she said. “If you can stop them and not have these ongoing threads of community transmission that have led us to be No. 1 in the country for COVID-19, it’s really important that we continue to test for the virus. We really have to make it so that people don’t have to stand in line for hours to get tested. We have to be much more nimble in being able to mobilize testing resources where they’re needed.”
Where we’re at right now ... is we don’t have a single proven case of reinfection (of COVID-19) yet.