How accurate is your rapid test now? Experts weigh in as Omicron fuels 6th wave

Medical experts say Canadians should keep a supply of rapid antigen tests handy as we head into a summer with almost no public health restrictions in much of the country. But experts add a negative result doesn't necessarily mean someone's in the clear.

Canada is already seeing a sixth wave of COVID-19 in the weeks after mask mandates and other measures lifted across the country. 

But while cases are on the rise, public PCR testing availability hasn't ramped back up after it became overwhelmed during the Omicron-driven wave that sent case counts soaring in January and February.

"I think using the rapid test prudently at home is what most Canadians will have to do," said Dr. Prabhat Jha, a global epidemiologist at St. Michael's Hospital in Toronto.

Jha recommends people use a rapid antigen test if they start showing COVID-19 symptoms, or if they had a high-risk exposure to an unvaccinated or symptomatic person with COVID-19.

Even then, he says, not all situations would necessitate taking a test.

Instead, Jha suggests considering: "Was the person that I had contact with vaccinated? Was the person actively symptomatic? Was it an indoor, closed space where I might have gotten a good load of their virus if they were hacking away?"

A positive result can also help an infected person get a better idea of the risk to their family members and others around them, especially as mask mandates lift and other respiratory viruses begin to circulate more, said Dr. Susy Hota, medical director of infection prevention and control at University Health Network in Toronto.

Regardless of a positive or negative result on a COVID test, both doctors say a person who is sick with a respiratory illness should isolate from others until they feel better. That way, they'll prevent passing on colds and flu, too.

Medical experts continue to warn that a negative result on a rapid test doesn't necessarily mean you don't have COVID-19. New Swiss research, which is yet to be peer-reviewed, suggests some rapid tests have "significantly lower sensitivity" to Omicron than to the Delta variant.

Similarly, research by Ontario's COVID-19 Science Advisory Table earlier this year found rapid tests are less sensitive for Omicron than Delta variant in nasal samples, especially in the first one-to-two days after infection.

Doctors now recommend isolating immediately after symptoms or exposure, then waiting a day or two before using a rapid test, to get the most accurate result possible from an increasing viral load.

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"By that time, the rapid tests are less likely to give you a false negative result," Jha says.