Skip to main content

Calgary pediatrician Jim Kellner is a member of the federal COVID-19 Immunity Task Force, which has helped inform government policy on infection and immunity issues.Todd Korol/The Globe and Mail

Rapid COVID-19 tests are widely viewed as a key tool for managing outbreaks, particularly among children as winter approaches and the highly infectious Delta variant remains the dominant strain in Canada.

Yet how best to use rapid tests, which can provide results in 15 minutes, continues to be debated, even among experts, because of their limitations.

Canada has a provincial patchwork of approaches regarding school settings; many put in place in recent weeks. That’s despite rapid testing now used broadly in workplaces, partly supported by the federal government, which has purchased and distributed millions of tests.

“So far, [rapid tests] have been used in adult settings to keep businesses open pretty successfully,” says Jim Kellner, a Calgary pediatrician specializing in infectious disease at Alberta Children’s Hospital and member of the federal COVID-19 Immunity Task Force, which has helped inform government policy on infection and immunity issues.

Dr. Kellner notes there’s little debate around the utility of these tests – more than 20 approved so far by Health Canada – including Abbott’s Panbio, which is used for screening unvaccinated workers and travellers. However, their effectiveness in screening large unvaccinated groups, like children ages 5 to 11, is less clear.

“The debate on these tests has gone on not only in Canada but all over the world for well over a year now, and it always has the same dimensions,” adds David Naylor, co-chair of the COVID-19 Immunity Task Force, contrasting Canada with the U.S., which allowed liberal use of rapid tests with uneven results.

Understanding the tests

The advantages of rapid tests, often called antigen tests, are they can be administered by a parent on a child, for example, involving a gentle nasal swab, while providing fast results onsite.

In contrast, the widely used PCR (polymerase chain reaction) tests usually involve an uncomfortable deep nasal swab, often administered by a nurse, with samples sent to a laboratory and results taking a few hours, at minimum.

“That rapid turnaround and relative ease” make rapid tests attractive in “the sniffle season,” Dr. Naylor says, especially among parents wondering if their child has a cold or COVID-19. He says some parents have banded together to buy large batches of tests in the absence of government policy.

While mostly accurate when symptoms are present, rapid testing is less effective in identifying viruses in asymptomatic populations with low disease incidence, Dr. Naylor adds.

That’s due to their tendency to produce false positives (results indicating disease when none is present) and, to a lesser extent, false negatives (results showing no virus present when it actually is), relative to PCR tests.

PCR tests, which can detect COVID-19′s genetic material, largely produce fewer false positives and false negatives and, as a result, are often required to confirm positive rapid test results.

Rapid test technology differs, detecting unique proteins on the virus surface – called antigens – and may not detect all asymptomatic cases when not much virus is present. Additionally, rapid tests are deemed to not have as high specificity – a scientific term for the ability to identify samples without disease – as PCR tests. As a result, rapid tests produce more false positives.

“How (rapid tests) perform in the real world depends on the prevalence in the population,” says Barry Pakes, program director for public health and preventative medicine at the University of Toronto’s Dalla Lana School of Public Health.

For example, for every 10,000 rapid tests in a population with a 0.1 per cent prevalence of virus (or 10 actual cases), there will likely be a few false negatives and hundreds of false positives, Dr. Pakes says. “So how it’s rolled out as a program is critically important.”

It’s why Dr. Pakes says rapid testing is more effective in helping control outbreaks in schools, or tracking virus spread in areas with high prevalence and low vaccination. Higher incidence results in more true positives relative to false positives, he explains.

How provinces differ on the debate

Despite agreement on this front, provinces have not taken similar paths using rapid tests. In Quebec, for example, they’re offered in schools, administered by staff for symptomatic, unvaccinated children. In Alberta, rapid tests have been made available for parents to test symptomatic children at home in outbreak areas, whereas in Ontario, the tests are now used in school outbreaks or in communities of high incidence in schools for asymptomatic, unvaccinated children.

In contrast, as of mid-November, B.C. had yet to offer rapid testing in school settings for children, while Manitoba only had only mandated testing for unvaccinated staff. Meanwhile, Saskatchewan and Nova Scotia have provided rapid tests to parents for children under 12.

“Despite efforts made to provide some broad framework federally, we never did seem to get national coherence on the way this shoul­­d be done,” Dr. Naylor says.

The situation in schools

He notes being “more of a hawk” for using rapid tests more widely for unvaccinated children than some colleagues, “but I fully respect those who are more cautionary.”

Dr. Kellner in Calgary points to new evidence suggesting rapid testing, despite its limitations, can be effective to control outbreaks. He points to a U.K. study, published in The Lancet in September, where some schools used rapid testing for seven days on close contacts in outbreaks while others had close contacts quarantine at home.

“Rapid testing worked just as well as quarantine at controlling outbreaks and kept a lot more children in school,” he says about the research involving students ages 11 to 18.

That’s important because false negatives, though less common, can lead to more spread. Even here, although antigen tests may miss more asymptomatic cases than PCR tests, research indicates those individuals typically have “non-infectious levels of virus,” Dr. Naylor says.

Systematic regimens, like those used in the workplace requiring two to three tests weekly, would likely find most infectious cases, Dr. Kellner notes.

With the approach of vaccines for ages 5 to 11, rapid testing’s use case will likely decrease with PCR remaining the key diagnostic for symptomatic cases, he says. Still, with children ages 4 and under remaining unvaccinated, rapid testing will remain important.

“At the very least, it should be offered so that parents can test symptomatic children at home and schools can test symptomatic children if they develop symptoms at school,” he says.

Debate aside, Dr. Kellner and other experts agree rapid testing technologies – already long used for pregnancy, for example – will only become more widely available as accuracy improves, and consumer awareness and demand grow, amid the realization the next pandemic is not a question of if, but when.

“This is the Fitbit generation, so it stands to reason these kinds of tests will become more commonplace.”

On Nov. 30, The Globe and Mail hosted a virtual event called Regenerative medicine: Where will stem cells take us? Presented by Bayer, the webinar explored the way researchers are working on stem cell advances that could change the future of medicine. Read more here.