Blood tests for the coronavirus could play a key role in deciding whether millions of Americans can safely return to work and school. More than 70 companies have signed up to sell so-called antibody tests in recent weeks, according to U.S. regulators. Governments around the world hope that the rapid tests, which typically use a finger-prick of blood on a test strip, could soon ease public restrictions by identifying people who have previously had the virus and have developed some immunity to it.
