Lateral Flow Tests Detect Most People At Risk Of Transmitting Covid-19

Routine testing to identify those infected followed by efficient contact tracing, and supported isolation is still the most effective public health measure we have to control Covid-19. Yet the US has never embraced testing as the powerful public health tool it could be in containing Covid-19.

Rapid testing has been unfortunately de-prioritized in the US in favor of unrealistic expectations placed on vaccines and has often been mischaracterized as less sensitive and therefore less effective in detecting Covid-19. However, a new study from Brigham and Women’s Hospital, University College of London, and Harvard researchers has found lateral flow tests are more accurate than previously reported and cannot be compared directly to how PCR tests work.

Covid-19 testing has traditionally focused on diagnosing symptomatic individuals using reverse PCR tests. However, mass antigen rapid lateral flow tests have recently been rolled out in several countries for regularly testing asymptomatic individuals as part of public health policy. The tests give a quick result using a device similar to a pregnancy test. It has been reported that in Europe some who live with high risk or immunocompromised individuals, even keep a stash of rapid tests by the front door and ask visitors to test themselves before entering their home.

Validation studies for lateral flow tests have mostly focused on comparing sensitivity, specificity, and predictive values to PCR tests. But the two tests work in different ways, lateral flow tests detect material from the surface proteins of the virus and are very likely to give a positive result when someone is infectious whereas PCR tests detect the virus’ genetic material, which can be present for weeks after a person is no longer infectious.

The study by UCL researchers published in Clinical Epidemiology uses a new formula that recalibrates relative performance statistics from Lateral flow vs PCR validation studies to give absolute sensitivity of lateral flow tests for detecting individuals who are shedding SARS-CoV-2 antigens. Using this formula the researchers found that lateral tests are more than 80% effective at detecting any level of Covid-19 infection and likely more than 90% effective at detecting those who are most infectious when using the test.

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Originally published on Forbes on October 22, 2021

© William A. Haseltine, PhD. All Rights Reserved.