In a new study, researchers found that testing half the population weekly with inexpensive, rapid-turnaround COVID-19 tests would drive the virus toward elimination within weeks— even if those tests are significantly less sensitive than gold-standard clinical tests.
Such a strategy could lead to “personalized stay-at-home orders” without shutting down restaurants, bars, retail stores, and schools.
The research was conducted by the University of Colorado Boulder and Harvard University scientists.
In the study, the team explored whether test sensitivity, frequency, or turnaround time is most important to curb the spread of COVID-19.
They scoured available literature on how viral load climbs and falls inside the body during infection, when people tend to experience symptoms, and when they become contagious.
They then used mathematical modeling to forecast the impact of screening with different kinds of tests on three hypothetical scenarios: in 10,000 individuals; in a university-type setting of 20,000 people; and in a city of 8.4 million.
When it came to curbing spread, they found that frequency and turnaround time is much more important than test sensitivity.
They also demonstrated the power of frequent testing in shortening the pandemic and saving lives.
In one scenario, in which 4% of individuals in a city were already infected, rapid testing three out of four people every three days reduced the number ultimately infected by 88% and was sufficient to drive the epidemic toward extinction within six weeks.
Sensitivity levels of COVID-19 vary widely.
Antigen tests require a relatively high viral load—about 1,000 times as much virus compared to the PCR test—to detect an infection.
Another test, known as RT-lamp (reverse transcription loop-mediated isothermal amplification), can detect the virus at around 100 times as much virus compared to the PCR.
The benchmark PCR test requires as little as 5,000 to 10,000 viral RNA copies per milliliter of the sample, meaning it can catch the virus very early or very late.
In the past, federal regulators and the public have been reluctant to embrace rapid tests out of concern that they may miss cases early in infection.
But, in reality, an infected person can go from 5,000 particles to 1 million viral RNA copies in 18 to 24 hours, said Parker.
The team says there is a very short window, early in infection, in which the PCR will detect the virus but something like an antigen or LAMP test won’t.
These rapid tests are contagiousness tests. They are extremely effective in detecting COVID-19 when people are contagious.
They are also affordable. The rapid tests can cost as little as $1 each and return results in 15 minutes. Some PCR tests can take several days.
The researchers say they are heartened to see that several countries have already begun testing all of their citizens, and hopeful that the new U.S. administration has named rapid testing as a priority.
One author of the study is Daniel Larremore, an assistant professor of computer science at CU Boulder.
The study is published in Science Advances.
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