Ms. Magnus, who has already completed a two-week quarantine at home, no longer cares if she gets her results. “By now, that doesn’t tell me anything,” she said.
Antigen tests, on the other hand, can be low-tech and easy to manufacture en masse. Distributed weekly or even daily, they could painlessly screen people headed back into offices, schools and universities, delivering peace of mind to parents, teachers and employers. Everyone — not just those feeling ill — would have an easier way to assess their health status on a regular basis.
“The goal here is to detect as many infections as possible,” said Daniel Larremore, an applied mathematician who models infectious diseases at the University of Colorado, Boulder. “That means taking as many shots on goal as we can.”
Broad distribution of antigen tests might also ease the demand for PCR, which still has an important role in hospitals and vulnerable communities like nursing homes. As things stand, many doctors still can’t get their patients’ results within 24 hours.
In those settings, accuracy is crucial, said Melissa Miller, director of the Clinical Molecular Microbiology Laboratory for U.N.C. Hospitals. “You don’t want to miss that diagnosis.”
There are drawbacks. Antigen tests will miss some people who would test positive by PCR, which amplifies coronavirus RNA and picks up even tiny amounts of it. With antigen tests, proteins can’t be copied in the same way, making it easier to mistake some people who are carrying minute levels of the coronavirus in their bodies as pathogen-free. Some antigen tests used in the past miss up to half the infections they look for.
Early on, many experts balked because of these shortcomings. “As laboratorians, we wanted the most sensitive test, the most specific test, the most accurate test,” Dr. Miller said. “End of story.”