The promise of antigen tests emerged like a miracle this summer. With repeated use, the theory went, these rapid and cheap coronavirus tests would identify highly infectious people while giving healthy Americans a green light to return to offices, schools and restaurants. The idea of on-the-spot tests with near-instant results was an appealing alternative to the slow, lab-based testing that couldn’t meet public demand.
By September, the U.S. Department of Health and Human Services had purchased more than 150 million tests for nursing homes and schools, spending more than $760 million. But it soon became clear that antigen testing — named for the viral proteins, or antigens, that the test detects — posed a new set of problems. Unlike lab-based, molecular PCR tests, which detect snippets of the virus’s genetic material, antigen tests are less sensitive because they can only detect samples with a higher viral load. The tests were prone to more false negatives and false positives. As problems emerged, officials were slow to acknowledge the evidence.
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