How rapid tests work and why timing is critical

With COVID-19 expected to be a part of our lives for the foreseeable future, new testing models are being developed that could help curb the spread of the disease.

How?

Health Canada has approved the first rapid antigen COVID-19 test, which can produce results in under 20 minutes.

That is much faster than the polymerase chain reaction (PCR) testing process currently in use across Canada. But it is also less sensitive than the PCR test.

Here's why that may not be a bad thing:

Because the rapid antigen test is not as sensitive, it will better detect a high viral load, explains David Juncker, a biomedical engineer at McGill University.

"There's increasing evidence that we need a high concentration of virus before we can actually infect someone else. And so, in that sense, the performance of this test is probably better tailored in finding people who are in an active infectious phase," says Juncker. 

"And so we could really break the chain and very quickly trace back," Juncker said. "Then block the spread in a much more efficient manner."

PCR testing remains the "gold standard." But the rapid antigen test could be a quickly deployable resource when timing is key, Juncker says.

"That delay is really important because when it takes three or four days to get the test, the other people might have infected many others."

WATCH | In the video above, biomedical engineering professor David Juncker explains how rapid tests work and the role they can play in curbing the spread of the virus.