https://www.scientificamerican.com/article/antibody-tests-for-the-coronavirus-may-not-change-everything/

British Prime Minister Boris Johnson called them a ‘game changer’. Antibody tests have captured the world’s attention for their potential to help life return to normal by revealing who has been exposed, and might now be immune, to the new coronavirus.

Dozens of biotech companies and research laboratories have rushed to produce the blood tests. And governments around the world have bought millions of kits, in the hope that they could guide decisions on when to relax social-distancing measures and get people back to work. Some have even suggested that the tests could be used as an ‘immunity passport’, giving the owner clearance to interact with others again.