Tough

Updated: November 1, 2020

When will a blood test be widely available to look for evidence of prior virus exposure?

Summary

Serology testing for SARS-CoV-2 is a blood-based test that can be used to identify whether a person has had prior exposure to the virus by looking for antibodies specific to COVID-19 [2,4]. Based on the limited evidence to date, serologic testing is not used routinely in clinical settings. The role of serology tests in clinical settings has not yet been confirmed and evidence is lacking to confirm that individuals are protected from reinfection of COVID-19 if the antibodies are present [5]. On May 12, 2020, Health Canada authorized the first COVID-19 serologic test for use in Canada [1] to help guide public health responses, by tracking rates of exposure and transmission in populations, geographic areas and workplaces, but not to determine individual levels of infection or immunity.  Currently, the COVID-19 Immunity Task force is collecting blood samples from large groups of individuals, which include asymptomatic or mildly symptomatic people who did not seek healthcare to provide the data needed to understand the scale of infection in Canada [3]. They are also currently conducting targeted population serological surveys which helps shed light on the immunity status of vulnerable populations [3]. In the next two years, Canada’s COVID-19 Immunity Task Force is hoping to collect and test at least one million Canadian blood samples to track the viral exposure in the general population and in specific groups at greater risk of having been infected (i.e. health care workers and the elderly) [1]. The performance of serological tests is analyzed by their sensitivity and specificity [4]. The sensitivity of a test describes its ability to successfully identify individuals who have SARS-CoV-2 antibodies (true positive rate), while the specificity of the test describes its ability to identify individuals without SARS-CoV-2 antibodies (true negative rate) [4]. The sensitivity of tests, approved by the FDA, currently range from 90-100% and the specificity range from 96-100%, indicating the possibility of an inaccurate result [4]. However, among multiple commercial assays for SARS-CoV-2 antibodies that are approved for use by Health Canada for serological testing, manufacturers for these tests have claimed approximately 95% sensitivity and 99.5% specificity [5]. The U. S. Food and Drug Administration (FDA) list of serological tests and their effectiveness is available here. It remains unknown, however, at this time how the presence of SARS-CoV-2 antibodies influences immunity to reinfection and the tests should therefore not be used as a test for SARS-CoV-2 immunity [5]

Contingencies

The development of a detailed, robust answer relies on several factors. To provide a detailed REAL Note requires knowing the following:

  • Population level studies to inform public health responses  
  • Ontario and/or  Canadian  decision making  and policy implementation  
  • Research  funding  allocated  towards  serological testing in Ontario  and/or  Canada  
  • Availability of testing and laboratory equipment, trained staff, and proper facilities 

Evidence

Review of Evidence

Resource Type/Source of Evidence Last Updated
Serology-based test for COVID-19
— John Hopkins Bloomberg School of Public Health: Center for Health Security
Report Last Updated: June 15, 2020
Serological Tests for COVID-19
— Canadian Agency for Drugs and Technologies in Health
Horizon Scan Last Updated: May 27, 2020
Statement from Health Canada on COVID-19 Serological Tests
— Government of Canada
Statement Last Updated: May 11, 2020
Research
— COVID-19 Immunity Task Force
Background Information Last Updated: June 25, 2020
EUA Authorized Serology Test Performance
— U.S. Food & Drug Administration
Report Last Updated: June 17, 2020
Disclaimer: The summaries provided are distillations of reviews that have synthesized many individual studies. As such, summarized information may not always be applicable to every context. Each piece of evidence is hyperlinked to the original source.

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