https://www.wired.com/story/researchers-push-for-mass-blood-tests-as-a-covid-19-strategy/

Next week, blood banks across the Netherlands are set to begin a nationwide experiment. As donations arrive—about 7,000 of them per week is the norm—they’ll be screened with the usual battery of tests that keep the blood supply safe, plus one more: a test for antibodies to SARS-CoV-2, the virus that causes Covid-19. Then, in a few weeks, another batch of samples will get the same test. And after that, depending on the numbers, there could be further rounds. The blood donors should be fairly representative of Dutch adults ages 18 to 75 and, most importantly, they’ll all be healthy enough for blood donation—or at least outwardly so.

Testing thousands of samples from seemingly-healthy people might sound a little wasteful, with all we’ve been hearing about testing shortages around the world. But that’s precisely the point, says Hans Zaaijer, a microbiologist at Amsterdam University Medical Center and Sanquin, the Dutch blood bank. He wants to see how many people have already had the disease and could possibly be immune.