a flood of new test kits hitting the market

4-28-20  Meanwhile a flood of new test kits with varying rates of accuracy is now hitting the market.  In the U.K., for example, Prime Minister Boris Johnson touted finger-prick antibody tests as a “game changer,” only for the government to realize that the 3.5 million tests it bought from China were not reliable enough to use.  Of particular concern here is the false-positive rate: If the prevalence of COVID-19 is quite low in the population—say, 5 percent—and a test can identify people who are truly negative with 95 percent reliability, half of the “positives” it returns will be false positives.  In other words half of the people the test says have antibodies wouldn’t actually have them.  “I wouldn’t want to tell a nurse or physician ‘Go back to work’ based on that,” Michael Osterholm, the director of the Center for Infectious Disease Research and Policy at the University of Minnesota, told me.

https://www.theatlantic.com/science/archive/2020/04/antibody-tests-herd-immunity/610762/