From The Atlantic:
As infections skyrocket, many Americans, like Dreifus, are clamoring once again for tests. Over-the-counter, at-home tests in particular have been flying off pharmacy shelves and out of online inventories, as companies scramble to scale up demand. People are turning to these tests when they feel sick, to avoid an onerous trip to a testing site or a doctor’s office or the days-long wait that tends to come with laboratory-based tests. At-home tests are also being heavily marketed as an option for folks who feel healthy to screen themselves before they venture out into the world.
But often, that’s not how people rely on rapid tests. “Using these one-off, for one event, is not watertight,” Alison Buttenheim, a behavioral scientist at the University of Pennsylvania who studies vaccines, told me. Negatives—even a pair of them—can’t guarantee that the virus wasn’t there, just that it wasn’t measured. And tests can’t predict the future if they’re taken days in advance of an event. Delta has a penchant for building to high levels in the airway, which does likely make it easy to detect, but it accumulates fast, so it might leave open only a small opportunity to pinpoint the virus before it hops into someone else. “It’s a tighter, earlier window,” Susan Butler-Wu, a clinical microbiologist at the University of Southern California, told me. Federal documentation for most rapid tests still calls negative results “presumptive,” noting that sometimes, it’s a good idea to confirm with a laboratory test.