Are COVID rapid tests still reliable with new sub-variants on the rise? What experts say

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Prime Minister Justin Trudeau said Monday that Canadians should get vaccinated against COVID-19 and influenza ahead of the winter to avoid the "danger" of needing other health measures this winter. He urged the inoculations to protect the health-care system from dealing with preventable admissions – Oct 17, 2022

As new COVID-19 sub-variants move across Canada, experts say rapid tests can still be considered an adequate tool to detect the virus – even if they are not perfect all the time.

“These tiny, tiny changes in sub-variants matter a lot in terms of the biological activity of the virus and its ability to escape our immune system, but rapid antigen tests aren’t nearly so easily fooled,” Colin Furness, infections control epidemiologist and assistant professor at the University of Toronto’s faculty of information, told Global News.

Rapid tests do have a tougher time recognizing specific spikes COVID-19 sub-variants create, but they’re still able to identify the virus itself, Furness explained. However, there are things to keep in mind in order to get an accurate result.

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When you test matters a lot as different variants of the virus produce different viral loads, Furness said.

“Now, it’s pretty hard to get a positive test when symptoms begin; usually you have to wait a few days,” said Furness.

“You can also have a negative test and still be infected, simply because you’re not contagious or not contagious enough to trigger a positive test.”

Swabbing not only your nose but your throat is the best way to properly test and get an accurate result amid swirling sub-variants, according to Furness.

Rapid tests detect a part of the virus called the nucleocapsid protein, according to Samantha Yammine, a science communicator in Ontario.

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“While these new sub-lineages of Omicron have a few different mutations in this part of the virus, it’s not anticipated that it will make rapid antigen tests no longer effective,” she told Global News.

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“But it may take more than one test to catch it, or it may take you being further along in your symptoms for it to be caught.”

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When assessing the impact of Omicron’s sub-lineages, like the highly-transmissible BF.7 currently surging through China where the virus was first detected, Public Health Ontario expects there to be a limited impact on rapid tests in the province.

“I don’t think we have evidence to suggest the rapid antigen tests we have are no longer useful,” said Yammine.

“I think they’re still useful for helping us navigate this phase of the pandemic when used properly.”

Although research is limited on rapid tests and COVID-19 variants of concern, that which has been done suggests that they still work.

While a study published in April in the Journal of Clinical Microbiology found the sensitivity in a rapid test may be altered with different variants, the most infectious cases should still be detected.

According to a study looking at the accuracy of rapid tests during the original Omicron variant, published in September in The BMJ, a peer-reviewed medical trade journal, only one out of three tests analyzed had a significant statistical decrease in sensitivity.

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The tests, known as Clinitest, is authorized by Health Canada to be manufactured in the country.

“Studies show that there is a reduction in sensitivity, but yet they’ve concluded that the remaining detection limit is good enough to detect those variants,” Dasantila Golemi-Kotra, an associate professor at York University’s faculty of science, told Global News.

With cases at a high last December, rapid tests began being distributed across the country. While some Canadians were unable to get their hands on a kit then, others were able to stockpile multiple.

Even as early signs show a resurgence of the virus this fall and winter, Golemi-Kotra doesn’t think Canada will find itself in a rapid-test rush again.

“I don’t think we’re actually going to see a situation we were in a year ago,” she said.

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But according to Don Sin, a respirologist at St. Paul’s Hospital in Vancouver and professor of medicine at the University of British Columbia, it’s better to be ready.

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“I think it’s far better to be prepared than be caught short-handed,” he told Global News, noting Canada currently has a robust stockpile of rapid tests.

Earlier this week, Canada’s chief public health officer Theresa Tam said she is preparing for the “worst case scenario” regarding COVID-19 variants.

Health Canada gave the green light earlier this month on the Pfizer-BioNTech booster shot that targets both the original Omicron variant and its BA.4 and BA.5 strains. Moderna’s updated booster was also approved in Canada five weeks ago.

Health Canada data shows in mid-September, 88 per cent of COVID-19 cases detected were BA.5, and nine per cent were BA.4.

As of Oct. 15, there were 21,188 cases of COVID-19 in the country, with Ontario having the highest count at 9,689, according to government data.

According to the World Health Organization on Wednesday, the virus still remains a public health emergency of international concern.

–With files from The Canadian Press

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