Still, the quick tests available now are frequently inaccurate. Although they ensure we can get an answer faster, said Dr. Ibukun Akinboyo, a pediatrician and infectious disease specialist at Duke Universitys School of Medicine, you lose some sensitivity, she said. Its hard to win at both.

Last month, a swab-based point-of-care test called Abbott ID Now made headlines when an analysis found that it might miss infections up to 48 percent of the time, despite being promoted by President Trump as highly accurate.

Sensitivity issues also plague antigen tests, which detect pieces of proteins made by the virus, rather than its genes. Antigen tests have been used to detect other airway infections, such as the flu, in less than an hour, and are easy to manufacture en masse. But the convenience comes at a cost: Unlike genetic material, antigens cant be amplified easily. Some antigen tests, including a few that search for influenza viruses, fail to pick up on active infections around 50 percent of the time.

If a Covid antigen test performs like an influenza antigen test, I dont think they will have much utility, said Dr. David Alland, the director of the Center for Emerging Pathogens at Rutgers New Jersey Medical School. Still, he noted, if improved, they could be very promising.

Even imprecise tests have their place in this pandemic, as long as theyre easy to use and distributed widely enough. Should a test miss someone on Monday, maybe youll get them a day or two later, Dr. Wyllie said.

So far, only two companies have received emergency authorization from the F.D.A. for coronavirus antigen tests. One is Quidel, which is, according to a representative, producing millions of tests each month, many of which have been distributed to urgent care centers and medical clinics in the United States. On Monday, a second firm, Becton Dickinson & Company, also entered the fray with a point-of-care antigen test that can reportedly produce results in 15 minutes. While speedy, both Quidels and BDs tests may produce false negatives between 15 and 20 percent of the time.

Other antigen tests have made headway overseas, and experts estimated that several more will likely seek clearance in the United States in coming months.

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A New Generation of Coronavirus Tests Is Coming. Here's What to Expect. - The New York Times