Over the past three years, many Canadians have grown accustomed to reaching for a rapid antigen test at the first cough or sniffle. Yet in March, the federal government stopped shipping COVID-19 rapid tests to provinces and territories. Now, millions of these tests are set to expire by December.
But experts say you should hold off on throwing out any rapid tests that have been collecting dust.
As new subvariants of SARS-CoV-2 emerge and infections climb across the country, there's still a need for rapid tests — even the expired ones.
Can we trust an expired positive rapid test?
Dr. Alon Vaisman, infectious disease physician at University Health Network in Toronto, explained: "It's true that over time, the test's ability to detect the virus slowly fades, but that doesn't mean it's entirely useless."
A handful of manufacturers of rapid tests available in Canada have even extended their shelf lives, which are brand-specific. For instance, Arton extended its test's shelf life from 18 months to 24 months.
Vaisman added even the expiry date indicated on the test's box or updated shelf life listed on the manufacturer's website has passed, people should "recognize that it's not useless to use that test."
What healthcare workers are more concerned about, Vaisman emphasized, are false positives and false negatives.
In an ideal scenario, someone infected with COVID-19 has a positive test and someone who doesn't has a negative test. But a "false positive" happens when your test indicates a positive result, even though you're not infected with COVID.
Because of this, you'll need to pay close attention to the control strip on your rapid test, said Vaisman. The control strip indicates whether the test is functioning correctly or not. A line on the control (C) and test (T) strip will appear if you test positive on a rapid test. Meanwhile, a single line on the control (C) strip indicates a negative result.
"If you see a positive control strip, you can say, 'Well, the control strip is positive, but my test is negative, so I have a little bit more confidence that this negative is a true negative.'" Whereas if the control strip doesn’t come up positive, that's a sign that your rapid test isn't functioning correctly, says Vaisman. "Then, the recommendation would be to retest using the same kit a few hours or a day later, or if necessary, take a formal test."
When to test for COVID-19 based on common symptoms?
According to Canadian guidelines, you should test if you exhibit symptoms or have been exposed to someone with COVID-19.
The most common symptoms of the Omicron wave are a runny nose, sore throat, headache and sneezing. According to the Public Health Agency of Canada, less frequent symptoms include fever, dizziness and a persistent cough.
Can rapid tests detect the new variants?
Experts say rapid antigen tests from one or two years ago can detect newer strains of the virus.
Based on what we know about how the test is performed, the areas it's testing for should be good at detecting new variants, explained Vaisman.
He added although Omicron — now the predominant variant — continues to evolve, older rapid tests can still detect its newer subvariants. Most rapid tests on the market are 'antigen' tests, which detect proteins on the surface of SARS-CoV-2 virus, separate from the spike protein involved in mutations.
Dr. Evans, chair of infectious diseases at Queen's University, agrees, adding the only difference is that Canadians will need to test daily for three consecutive days.
"Omicron reduced the sensitivity of the test, meaning that a negative test done once does not reliably tell you that you're not infected, which is one of the reasons we recommend you test daily for three days," Evans said. "Doing that increases the test’s sensitivity."
How to make sure the rapid tests you have don't go bad?
There's more to ensuring the accuracy of a rapid test than its expiry date. How you store your tests also makes a difference.
Experts advise Canadians to avoid stashing rapid tests in your car's hot glovebox or refrigerator. A better place to store rapid tests would be in your bedroom closet or bathroom cupboard, ensuring the temperature is between 2 and 30 degrees Celsius.