Vaccinated Canadians can have COVID-19 symptoms despite testing negative. Here’s why

Experts say a person may test negative for COVID-19 on a rapid antigen test despite being infected, partly due to how quickly vaccination clears the amount of virus in their body.

As Canada heads towards a sixth wave of COVID-19 with rising cases and hospitalizations across the country, experts say people can still test negative on a rapid test in the first few days they have symptoms.

This is partly due to how quickly vaccination clears the amount of the virus in an infected person’s body.

“If the antigen test is dependent on the amount of virus in your upper respiratory tract, you will still be infectious … in the first few days,” said Dr. Earl Rubin, an infectious disease specialist and a division director of pediatric infectious diseases at the Montreal Children’s Hospital.

“But you may clear the virus more rapidly if you have good antibody from the vaccine … and therefore the antigen test may become negative quicker in those who are vaccinated rather than the unvaccinated,” he added.

Rubin explains that how quickly a vaccinated person clears the virus doesn’t necessarily mean that rapid antigen tests aren’t working.

“Antigen tests are available and (they’re) fast … You don’t have to leave your house, you can do it yourself. So there are a lot of advantages, but I think people have to really understand the limitations of the tests,” he said.

Rubin adds there’s a debate among health experts on whether antigen tests may not be as sensitive to the newer variants of COVID-19, like Omicron.

“It’s hard to compare in real time … because antigen tests weren’t as readily available or used as much as they are now, but they certainly do work,” he said.