Rapid Antigen Screening

Written By CDL Rapid Screening Consortium (Super Administrator)

Updated at March 23rd, 2021

The Challenge

COVID-19 is an unprecedented health crisis. We need to dedicate our energies to making sure people are protected from disease.

From an economic perspective, it is an information problem. Work and social life is not safe because we do not know who is infectious. This causes us to treat everyone as infectious by social distancing, wearing protection and cyclic lockdowns.

Solving the information problem requires information. If we can tell who is likely to be infectious, we can isolate them and protect others. 

The State of Play

Governments have taken steps to address the information problem. But their priority is identifying people who are infected with COVID-19 so that they can be treated expeditiously. 

There is currently a testing system in place whereby people who are suspected of being infected with COVID-19 can obtain verification of it. This laboratory based molecular testing (called polymerase chain reaction (PCR) testing) is available and is considered by public health authorities to be the “gold standard” in COVID-19 testing but it requires a health professional to administer the test, with results available within 24 and 48 hours.  

This is supplemented with a system of contact tracing that is triggered once a person is diagnosed with COVID-19. That system looks to identify that person’s contacts and to notify and evaluate them as being potentially infected with COVID-19.

Depending on the prevalence of COVID-19 in a region, these testing and tracing resources can be limited.

Screening vs. Diagnostic Testing

Diagnostic testing relies on laboratory-based quantitative PCR tests that can detect minute amounts of viral RNA connected to SaRS-CoV-2, the virus that causes COVID-19. PCR testing cannot be scaled in order to meet the demands of widespread testing strategies. Rapid antigen tests detect SaRS-CoV-2 proteins directly. Rapid antigen tests are known to have lower analytical sensitivity (the ability of a test to correctly identify patients with a disease) but achieve similar specificity (the ability of a test to correctly identify people without the disease) results to those of PCR tests.

Review our selected list of Explainers and Scientific Studies as additional resources to better understand the difference between rapid antigen screening and diagnostic testing.

The Opportunity

New ways of being able to determine whether a person is infectious have been developed. These measures differ from PCR tests in that, rather than identify the genetic markers of COVID-19, they identify specific proteins associated with COVID-19 infection. These markers are antigens.

It is easier to determine whether a specific antigen is present in an individual. That means that antigen screens are:

  • Rapid: the results from antigen tests are typically available in 15 minutes or less. 
  • Cheaper: whereas PCR tests might cost between $60 and $250 to administer in Canada, antigen screens can cost less than $10.
  • Targeted: antigen screens are calibrated to determine whether a person is likely infectious. While these may not determine whether someone is infected with a low viral load of the coronavirus, they are sensitive in determining whether someone is likely infectious.

These three factors mean that rapid screens can be applied at our workplaces to monitor people frequently, break chains of transmission and make those places safer. 

Note: Public health authorities have issued guidance which states that rapid antigen testing should be used for screening purposes only and should not be used for diagnosis of acute COVID-19 infection. Public health authorities have issued guidance stating that any positive results from rapid antigen screening must be confirmed with laboratory-based testing. 

Rapid antigen testing does not replace public health measures such as symptom screening, physical distancing, hand hygiene, the use of face coverings or the requirement to protect the health and safety of workers.

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