Walk-in health provider CityMD had to backtrack in recent days after it misled thousands of customers into thinking they were immune to COVID-19. Some 15,000 people who tested positive for novel coronavirus antibodies—which may indicate past infection but do not definitively offer any kind of guarantee of immunity—were told online, where they got results, that they were in the clear. The company said the whole flap was the product of an editing error, and apologized for the oversight. But it risked feeding a larger perception that antibody, or serology, tests are a sort of silver bullet that confer protection—and the OK to breach social distancing.

Antibody testing has expanded in New York in recent days, thanks in part to an NYC initiative to make it more wildly available. But it seems valuable, for now, mostly as a way to chart the spread of infection across demographics.