Understanding the role of the Rapid Antigen Test

As PCR testing resources have been unable to keep up with demand across the country, rapid antigen tests (“rapid tests”) have become an important tool in the pandemic. These rapid tests, which can be done at home, among other places, have been helping more Canadians find out quickly (within 15 minutes) whether or not they have the SARS-CoV-2 virus, or more importantly, whether they are infectious. Here, CoVaRR-Net experts look at the science and practice of rapid tests and give advice on how and when to use them, how they can help stop super-spreader events and how they may be part of our lives even after the pandemic has ended.

How and when to take Rapid Antigen Tests

Rapid tests are recommended when you:

• have symptoms;
• suspect exposure to COVID-19;
• don’t suspect exposure but will be attending a large gathering;
• are completing an isolation period and want to check if you’re still infectious;
• have been in a location that has experienced an outbreak;

Timing

Rapid tests are a screening tool and have more value when used correctly, at the correct time, and more than once.  If availability is not an issue, doing multiple tests to confirm results is recommended by many researchers. Dr. Cory Neudorf, CoVaRR-Net’s Public Health, Health Systems and Social Policy Impacts Pillar Co-Lead says it’s important to take the test in a specific time window after possible exposure to SARS-CoV-2 (the virus that causes COVID-19).

“When it comes to rapid antigen tests, they need a certain amount of viral load to give a positive result. The viral load builds to detectable levels between day 2 and up to 10 days after exposure or experiencing symptoms, whichever is earliest. It’s in that time window that the rapid antigen tests can be most helpful,” says Neudorf. He adds that if you’re in the early stage of the disease and are asymptomatic, you could still be shedding the virus and spreading it to others. “It’s important to limit your contacts immediately if you have been exposed to someone with COVID-19.”

Tips on getting an accurate result

There have been some public health suggestions recommending blowing one’s nose before administering the test. Neudorf says there is no real need for that, as it does not make the virus more detectable. “But there have been studies that have shown better results if you squeeze your nose as you remove the swab.”

He also adds that when self-administering the test, you need to make sure to tilt your head and reach far back into the nostril with the swab, rather than simply reaching upward into the nose. And he cautions not to swab too vigorously, as you can cause a nosebleed and contaminate the sample.

There have also been studies suggesting that a combination of swabbing both the throat and nose has been more effective in picking up virus particles, with at least one province, Nova Scotia, recommending that both the throat and nose be swabbed. The efficacy of this practice, however, is still under active investigation by scientists, with most jurisdictions evaluating it.

Recommendations on how rapid antigen tests can be used to help Canadians through this pandemic

Public locations that can benefit from rapid-test screening

With limited supplies of rapid tests, it’s important to use them as effectively as possible.

Homeless shelters, care-home facilities, and hospital emergency rooms can greatly benefit from rapid tests as screening tools. The tests can also be employed to screen in places where an outbreak has occurred, such as a school.

People without symptoms should also use rapid tests when going into a populated area, to avoid super-spreader events.

“Rapid tests are particularly good before attending large events and gatherings, along with the use of masks,” says Dr. Nazeem Muhajarine, CoVaRR-Net’s Public Health, Health Systems and Social Policy Impacts Pillar Co-Lead. “Even if you don’t suspect you have COVID, taking a rapid test is smart before going to a populated area, especially if visiting people who might be particularly vulnerable. You need to ensure you are not unknowingly spreading SARS-CoV-2. And anyone who has been exposed to a COVID-19 case should not attend these gatherings at all, even if the test is negative.”

Improving the reporting of rapid test results

The reliance on rapid tests as both a screening and diagnostic tool without formally reporting (positive) test results to public health officials skews both clinical and public health case numbers.

“We need to develop a formal mechanism to connect at-home test results to provincial public health units,” says Dr. Cheryl A. Camillo, who is leading the study and development of recommended policy responses to mitigate the impact of the pandemic at COVaRR-Net. “It’s important that provinces and territories know the full extent of the spread of COVID-19 in their population in order to make evidence-informed decisions to protect their residents.”

Rapid tests will be around for a long time

All three researchers believe we should get used to rapid tests, as they will likely remain well after the pandemic. “We may see the expansion of these tests for people to self-test for other kinds of viruses such as influenza,” suggests Dr. Neudorf. But for COVID tests, he adds, that how long into the future they will be used will depend a lot on how long governments will subsidize their sales.

To arrange an interview with Dr. Cory Neudorf, Dr. Naseem Muhajarine or Dr. Cheryl Camillo, please contact:
media@covarrnet.ca