In Doubt: Reliability of Rapid Tests in Early Days of Omicron

A resident inserts a nasal swab into a test tube while in line at a Covid-19 testing site run by the Centers for Disease Control (CDC), Federal Emergency Management Agency (FEMA) and eTrueNorth in Washington, D.C., U.S., on Wednesday, Jan. 5, 2022. The U.S. recorded over a million coronavirus cases on Monday, nearly doubling the previous records with hospitalizations increasing fueled by the virus rapidly spreading among the unvaccinated. Photographer: Eric Lee/Bloomberg via Getty Images
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A resident inserts a nasal swab into a test tube while in line at a Covid-19 testing site. - Photographer: Eric Lee/Bloomberg via Getty Images

At-home antigen tests, already in short supply, may be unreliable in detecting Omicron in its early days, a new preprint study finds.

The small but consistent study looked at 30 people who were tested daily with both rapid antigen tests and more sensitive PCR tests. Despite producing positive PCRs, in all cases the antigen tests produced false-negatives for 2 days.

That raises alarms about transmission: In at least 4 confirmed cases, infected people transmitted the virus before showing a positive result on an antigen test—though many other transmissions likely occurred, researchers warn.

The tests still work, researchers said—they just may not detect the virus in its early phases, limiting their usefulness as a screening tool for gatherings or work, and meaning “we will be unable to effectively test our way out of the current surge,” one researcher said.

Swabbing saliva may be more effective: The study found that viral loads peak in saliva 2 days before peaking in nasal swabs—building on evidence that saliva swabs may be better for detecting Omicron.

The Quote: “I think that with every new variant that comes, scientists have to question whether the things that were previously true are still true. This one has a different way it travels, a different mechanism of action of symptoms, it has different windows of transmission,” said lead author Blythe Adamson.

STAT News


Related: 

There's one crucial step to your Covid self-test you may be missing, experts say — CNN

Flooding emergency rooms, calling 911: Texans are going to great lengths to find COVID-19 tests — Texas Tribune

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