Quick Less Precise, but Repeated, Covid-19 Tests Can Be Better Than Slow Precise Tests

(p. A1) Public health experts are increasingly calling for a shift in thinking about Covid-19 testing: It is better to get fast, frequent results that are reasonably accurate than more precise results after dayslong delays.

. . .

Covid-19 tests that don’t require a lab tend to be less sensitive than “gold standard” laboratory-based tests, meaning they are likely to miss more cases. But many public health experts now say that repeat testing can make up for the loss of sensitivity, and such testing could quickly identify the most infectious people and help bring transmission to heel as workplaces and schools resume in-person operations and as influenza season looms.

. . .

(p. A6) “When we looked ahead, we realized we needed a paradigm shift from the still-needed diagnostic tests to the screening tests,” said Jonathan Quick, managing director for pandemic response, preparedness and prevention at the Rockefeller Foundation, which released a report in July [2020] calling for a massive scale-up in quick, cheap tests for Covid-19 screening. “As a practical matter, that meant making much more of a new kind of test,” Dr. Quick said.

Most Covid-19 diagnostic testing in the U.S. is processed in laboratories and uses a technique called rt-PCR that searches for the virus’s genetic material and amplifies it. The tests are incredibly sensitive but expensive to run, and the process often requires shipping samples from a test site to a lab.

. . .

“I think there’s a sense of desperation that we need to do something else,” Ashish Jha, dean of Brown University’s School of Public Health, said at a media briefing in August [2020].

. . .

Antigen tests are better at identifying cases when people have more virus in their system—meaning they will likely find people when they are most infectious, said Michael Mina, an epidemiologist at the Harvard T.H. Chan School of Public Health and an advocate of low-cost, widely available at-home testing that can be done on a paper strip.

. . .

The FDA also has said that rapid tests should have comparable accuracy to PCR diagnostic tests—a requirement that some public health specialists and companies say is overly stringent for surveillance testing.

An FDA official noted sensitivity rates lower than PCR might be acceptable, depending on how the test results are used. The agency has allowed for antigen tests with a sensitivity rate of 80% or better, the official said. “You can even have lower than 80% sensitivity” if it is a recurring or serial test.

For the full story, see:

Brianna Abbott, and Thomas M. Burton. “Speed Over Precision Favored in Covid Tests.” The Wall Street Journal (Wednesday, September 9, 2020): A1 & A6.

(Note: ellipses, and bracketed year, added.)

(Note: the online version of the story has the date Sep. 8, 2020, and has the title “Public Health Officials Pursue Covid-19 Tests That Trade Precision for Speed.” Where there are differences between the print and online versions, the passages above follow the online version.)

The report by The Rockefeller Foundation mentioned above is:

The Rockefeller Foundation. “National Covid-19 Testing & Tracing Action Plan.” Thurs., July 16, 2020.

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