Random testing at Canada’s border can’t distinguish between people who previously had COVID-19 and those currently infected by it, according to a statement from the government received by Global News.
The mandatory measure, which affects roughly 1 in 20 fully vaccinated people who enter Canada by air, is also leading to healthy travellers being forced to quarantine.
The tests being used — PCR or molecular tests — are too sensitive to tell the difference between active infections and previous infections.
Still, the government insists on using these tests because it says they’re the “gold standard” for detecting the virus, even if they may be catching people who fully recovered from it.
“You’re shooting at a dartboard with a blindfold on,” said Colin Furness, an infectious disease specialist and epidemiologist at the University of Toronto.
“I want us to do disease surveillance. I want us to do transmission control … but I don’t think their current plan is actually particularly effective at either of those things.”
Mandatory random testing of fully vaccinated travellers began in late 2021 to help monitor the spread of new variants entering Canada and to make sure infected travellers quarantined.
Roughly 5,000 people are selected each day, according to the government. Tests are performed by a handful of private companies who have received hundreds of millions of dollars in government contracts since the start of the pandemic.
Random testing was widely criticized this spring as a source of unprecedented disruptions at Canadian airports. Critics said it was leading to bottlenecks at customs checkpoints, which created cascading problems leading to flight delays and cancellations.
The government paused testing at airports in mid-June to ease some of these pressures. But in the interest of continuing to track new variants, restarted the program a month later, with tests either self-administered at home or completed at locations outside airports.
Denise Chenier, who lives in San Francisco and recently travelled to Canada with her husband, Grant, was one of those selected for testing at Toronto’s Pearson airport after the program restarted.
The couple was flying to Thunder Bay to settle the estate of Grant’s mother and to celebrate her life.
The Cheniers got to Thunder Bay on a Saturday in late July, the same week random testing resumed. Denise completed her PCR test the following Monday, which is when she said the government-contracted lab opened. She said several more days went by without getting the results.
When she contacted public health officials to get the results, she said she was shocked to find out it was positive and that she needed to isolate for 10 days.
“I read it and I thought, ‘That’s a typo.’” Denise said.
The couple had recently recovered from COVID-19 and had both tested negative on multiple rapid antigen tests completed during a 12-day isolation period leading up to their trip.
They said it’s unlikely they were reinfected with the virus before travelling because they limited contact with others, wore masks at all times, and had two booster shots each.
They also said that they performed rapid antigen tests after arriving in Thunder Bay and that the results were negative.
The couple said they explained their situation to local, provincial and federal health officials over the phone, all of whom agreed the test likely picked up Denise’s previous infection.
But rules are rules, Denise said she was told, meaning she still needed to quarantine.
“This was a huge imposition,” Grant said. “A waste of time and money.”
Scope of testing
The government said all fully vaccinated travellers who enter Canada have an “equal chance” of being selected for random testing. It doesn’t matter which country a traveller is coming from, how long they were away, or if they’ve been selected for testing before.
The government said its daily target of roughly 5,000 tests was set to make sure it has a “representative, reliable and robust estimate” of the number of people who are positive for COVID-19 at the time they cross the border.
But the government also said its tests can detect previous infections for up to 180 days, which means many of the positive test results could be old infections, as opposed to active infections.
To avoid potential problems, including forcing people with previous infections to needlessly isolate, anyone who provides a positive PCR test result taken up to 180 days before entering Canada is exempted from the random testing program.
But access to PCR testing has been limited in many places over the past year, meaning it’s unlikely travellers with previous infections will be able to provide the proof they need in order to get an exemption.
The Cheniers, for example, were told by their family doctor to not bother with a PCR test because they had many symptoms of COVID-19 and because they tested positive on rapid antigen tests.
The couple said they support testing at the border, but think the exemption to random testing should be extended to anyone who previously tested positive on a rapid antigen test.
In Ontario, meanwhile, access to PCR testing was restricted to “high-risk” individuals in December 2021. Anyone who wasn’t considered high-risk and had symptoms of COVID-19 was told to “assume” they had the virus without getting a PCR test. The provincial government also expanded access to rapid antigen tests through workplaces and pharmacies.
James Hay, a postdoctoral research fellow at Harvard’s Center for Communicable Disease Dynamics, said it’s “exceedingly unlikely” anyone would test positive for COVID-19 six months after an infection.
He said research has shown most people will begin to show negative results on a PCR test between 10 and 14 days after infection.
Hay also said rapid antigen tests, which are less sensitive than PCR tests, would be a more effective tool for detecting active cases of COVID-19 at the border.
“An antigen test is actually very specific to that potentially infectious period because you have to have a lot of the virus to turn an antigen test positive,” he said.
A useful method for doing this would be to give travellers two or three rapid antigen tests and ask them to complete the tests over several days, Hay said.
Anyone who repeatedly tests negative likely won’t be infected with the virus, Hay said. Those who test positive are likely in the midst of an active infection and can be targeted for follow-up.
“There’s still definitely a role for testing, it’s just where it’s done and how often it’s done is probably changing,” Hay said.
Benefits of PCR testing
A major benefit of using PCR testing is that it allows for “sequencing” of the virus, which is necessary to distinguish between different variants, Hay said.
This allows the government to monitor the spread of emerging variants, such as Delta and Omicron, and potentially ward off any serious threats to Canada by imposing new public health measures.
This could include restricting flights from countries where data shows more contagious and potentially deadly variants are spreading or imposing stricter quarantine measures for international travellers.
“It might be an early warning sign,” said Caroline Colijn, a mathematics professor at Simon Fraser University and an expert in infectious disease evolution.
Colijn, who was on the federal government’s COVID-19 expert advisory panel, said it’s important to understand the objectives of any testing regime before determining its effectiveness.
From the perspective of monitoring new variants, she said, the government’s random testing strategy at the border is useful.
But when it comes to preventing transmission of the virus, the strategy isn’t doing much, she said.
That’s because the number of people tested at the border is low and because there’s already “widespread transmission” within Canada.
“We’re not preventing most transmission events,” Colijn said.
Statistics from early in the pandemic, when provincial governments were still regularly reporting daily infection figures, show less than two per cent of COVID-19 cases in Canada are linked to international travel.
Colijn said there is not much added benefit in forcing fully vaccinated travellers who test positive on a random PCR test to isolate.
Still, she said, the government simply ignoring a positive test result at the border, even if it’s from a previous infection in a person who’s likely no longer contagious, could be seen as irresponsible.
“Now that you know, you should probably do something to prevent onward transmission,” she said.
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