Testing for COVID-19 and tracing the prior contacts of those found to be infected are crucial measures for slowing the disease's spread, but inadequate unless combined with other measures, researchers said on August 19. By itself, the test-and-trace approach can reduce the virus' reproduction rate, or R number, by 26 percent, they reported in The Lancet Infectious Diseases, using mathematical models to examine data from previously published studies.

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The reproduction rate measures the number of people in a population, on average, infected by each person carrying the virus.

Anything above "1" means the disease is continuing to expand; below that threshold, it will eventually peter out.