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COVID-19: Experts weigh in as B.C. prepares to address its rapid test lag

‘In an ideal world, we would distribute them to as many people as possible’
A traveller stops to be tested for COVID-19 at the testing centre for arriving international passengers at Vancouver International Airport, in Richmond, B.C., on Thursday, December 2, 2021. THE CANADIAN PRESS/Darryl Dyck

Moira Wyton, Local Journalism Initiative Reporter THE TYEE

As the highly transmissible Omicron variant takes hold, British Columbia is one of the only provinces that has not yet made rapid antigen tests widely available to the public.

Rapid tests can be administered at home and measure whether someone has COVID-19 and is likely to infect others. They return results in as little as 15 minutes.

B.C. has received three kinds of tests from the federal government: Abbott ID Now, Abbott PanBio and BD Veritor. None are packaged for use at home.

But some 700,000 testing kits could be deployed for individual use, provincial health officer Dr. Bonnie Henry has agreed, if boxes were broken down into smaller kits with extra swabs and solution, as Nova Scotia has done with BD Veritor tests.

As of Dec. 3, B.C. had sent out almost two million of the more than 3.2 million tests it had received from the federal government. About 315,000 tests had actually been used.

Health Minister Adrian Dix said last week the province uses 35,000 tests weekly. The tests are currently available to select businesses, non-profits and charities through the province, and are being used in some remote communities where access to lab-based testing is limited.

British Columbians can also purchase at-home rapid test kits for about $40 each at certain pharmacies, while prices for similar kits online have soared.

Independent experts and doctors in B.C. have long called for rapid tests to be a bigger part of the province’s strategy, while Henry has downplayed their usefulness.

“Ideally, they should be made available freely,” said Dr. Lyne Filiatrault, a former emergency physician who helped avert the SARS epidemic in Vancouver.

“It is an additional layer of protection we will have to use in B.C.,” she added during a briefing last week with Protect Our Province BC, a group seeking increased testing and faster booster rollouts.

On Tuesday, Henry and Health Minister Adrian Dix unveiled a new strategy to distribute rapid tests more widely to the public in the New Year.

RELATED: Rapid testing to expand; return of mass-vaccination sites for COVID booster shots in B.C.

In advance of that, the Tyee spoke to three experts about how rapid tests can be used to keep individuals and communities safer.

How do they work?

There are a variety of rapid antigen tests that all measure whether someone with COVID-19 is infectious to others. They do this by measuring whether one’s viral load — how much the virus has replicated in one’s body — is past a certain threshold when the test is taken.

That means that rapid tests don’t catch everyone who has been infected with the virus but focus on the subset of infected people who are contagious to others.

By contrast, molecular polymerase chain reaction or PCR tests can detect the virus at much lower levels, before, after and during someone’s infectious period.

B.C. is also asking people only to get PCR tested if they have been exposed or develop symptoms, with long lines for many testing sites in Vancouver being reported as the fifth wave ramps up.

Rapid tests are useful in part because some people can be infectious without symptoms. Vaccinated people can still transmit the virus, although at a much lower rate than unvaccinated people. Early evidence also suggests two doses of vaccine are significantly less protective than three against the Omicron variant compared to Delta.

Filiatrault said about 60 per cent of transmission of COVID-19 happens when someone is asymptomatic, so rapid tests can help identify more people at risk of infecting others.

“It lowers the risk that you will be transmitting to anyone else,” said Dr. Victor Leung, an infectious disease physician in Vancouver. “What it doesn’t say is that you will be clear from COVID-19 for the next day or few days.”

How accurate are they?

The accuracy of rapid tests is quite high in terms of identifying someone likely to infect others, regardless of whether they have symptoms.

The tests will return a positive result, on average across all brands, for 97 per cent of people who could likely infect others.

For people with viral loads that make them not likely infectious, rapid tests will be positive between 19 and 63 per cent of the time.

False positives occur in about one to three tests per thousand.

PCR tests, which are required to confirm illness if someone receives a positive rapid test result in B.C., are upwards of 99 per cent accurate but can take days to get results back depending on lab capacity.

Henry has repeatedly said that rapid tests provide limited benefit when used regularly in the community among vaccinated, asymptomatic individuals, producing few positive results.

But Leung said just because rapid tests may identify relatively few cases compared to PCR tests, which are only for symptomatic or exposed people, doesn’t mean they’re useless.

“If the numbers are so low .125with rapid tests.375 that you show most people are negative, it gives you more information,” said Leung. “But if you’re positive, you could potentially avert a significant superspreading event which would then bring up transmission rates in the community.”

How should we use them in BC?

Leung, Filitrault and University of Calgary researcher Gosia Gasperowicz all agree that rapid tests could help British Columbians have more confidence doing things like working and visiting relatives for the holidays.

Leung said because viral loads change quickly as the virus replicates, they are best used directly before seeing family or heading out to work.

And with Omicron showing evidence that it replicates much more quickly than Delta, rapid test results should be taken as snapshots in time of one’s infectiousness.

“The most effective way to view rapid tests in general, is that they are another tool we have that can provide a higher level of certainty in the short term, like eight to 12 hours, that you are unlikely to be infectious with COVID-19,” said Leung.

Gasperowicz said they also shouldn’t be used to justify going to concerts, large social gatherings or other high-risk settings.

“It is not a free pass to do more,” said the developmental biologist and a researcher at the faculty of nursing at the University of Calgary. “It’s something that allows you to do with more confidence what you would do anyway.”

All three experts said other precautions, like good ventilation and quality masks, should be taken when indoors with others.

Leung said rapid tests can help health-care workers determine if they are infectious as Omicron places more pressure on the system.

Schools and other environments at high risk of superspreading should also have priority access to rapid tests. B.C. has used the tests in a number of outbreak settings already, including the ongoing outbreak at the University of Victoria.

The experts agree the best approach would be to make free rapid tests available widely to the public, allowing people to test themselves each day and make decisions on their activities.

“In an ideal world, we would distribute them to as many people as possible and follow that distribution with very clear education and communication so it minimizes the chance they are misunderstood and misused,” said Leung.

RELATED: Think you have COVID-19 during the Omicron wave? Here’s what to do