Are Rapid Tests Still Effective During Flu Season and COVID-19 Variants?
With the upcoming fall flu season and the ongoing spread of new COVID-19 variants across Canada, attention is once again turning to rapid antigen tests. However, this flu season presents new challenges as the federal government has stopped shipping rapid tests to the provinces and territories. As a result, Canadians may have to search harder or even pay out of pocket to find these tests, according to experts.
In light of the limited supply, increasing numbers of expired tests, and the emergence of new COVID-19 variants, the effectiveness of rapid tests comes into question. Dr. Gerald Evans, an infectious disease specialist at Queen’s University, explains that there is still value in these tests because the virus that causes COVID-19 sheds for longer periods than other respiratory infections. Rapid tests can provide information on how long someone may need to be off work due to COVID-19.
The federal government discontinued shipments of rapid antigen tests in March 2023, stating that there was enough supply in the provinces and territories. Health Canada reported that it had ordered over 811 million rapid tests since the start of the pandemic, with approximately 680 million distributed to provinces and territories. However, 6.5 million tests will expire this year, with the rest expiring within two years.
Can expired rapid tests still be used? According to Nazeem Muhajarine, a professor of epidemiology at the University of Saskatchewan, rapid test kits are likely still effective for 15-20 months past their expiry date. He even used a test that expired in May on a family member. Muhajarine believes that expiration dates are often conservative and that proper execution of testing instructions, such as thorough swabbing and correct storage conditions, is more crucial.
Health Canada clarified in an email that the expiration dates and shelf life of rapid antigen tests depend on the specific brand. The authorized shelf life (without extensions) can be found in the testing information section of Health Canada’s list of authorized testing devices. Manufacturers conduct extensive research to establish an estimated shelf life and expiry date for their tests. Companies establish these dates based on data collected to demonstrate that the tests will continue to perform as intended.
While some manufacturers have conducted studies on the accuracy of their rapid tests after the expiry date, their sensitivity may decrease over time. A positive result on an expired test is still reliable, but negative results may be less accurate. Dr. Evans recommends repeating the tests over three consecutive days to improve accuracy, especially for those feeling unwell but receiving negative results.
Regarding the effectiveness of rapid tests against new variants, early data suggests that they can detect the Omicron variant. However, there may be reduced sensitivity. Dr. Evans states that current tests may be less sensitive to the lineage variants, such as EG.5 and BA.2.86. To overcome this, experts recommend performing additional tests if feeling unwell and receiving a negative result.
While the spike proteins of the virus may mutate, the antigen-based test kits are designed to detect a specific marker associated with the virus (nucleoprotein). This marker does not typically mutate, which means the tests should still work effectively against new variants.
As for where to find rapid antigen tests in Canada, pharmacies and grocery stores are good places to start. However, due to the limited supply, stores may begin charging for them. Dr. Evans suggests checking with provincial public health authorities to find out where to obtain the tests.
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