The value of antigen tests is based on a simple tradeoff. They’re not as sensitive as polymerase chain reaction (PCR) tests, which are the gold standard for diagnosing COVID-19, but they’re most effective when people with the virus are most infectious. And since they’re cheaper, faster, and easier to perform, the ability to do more tests can balance out the lower sensitivity. If their convenience means you take eight antigen tests a month, versus, say, two PCR tests a month, the antigen regime might catch cases that the PCR regime misses. One recent analysis suggests that using antigen tests on a population three days a week would be virtually as effective in catching infections as using the superior PCR test the same number of times.
But for an effective antigen-testing plan to work, the tests have to be given frequently and the results quickly reported. While PCR tests are done at labs, which are practiced in reporting results to health agencies, antigen tests are intended for places such as schools and nursing homes, which have to develop their own reporting systems. And that’s been a problem since the tests started going out in May. By August, the test manufacturers Quidel and BD combined to produce 3 million antigen tests a week. But by mid-September, states had reported only 215,000 antigen-test results. There was, as The Atlantic’s Alexis Madrigal and Robinson Meyer wrote then, “a hole where data about antigen testing should be.” At the time, only six states made antigen-testing numbers available (now 20 states do), and extrapolating those results suggested that only 1.4 million antigen tests had been conducted nationwide.
The federal government pressed on with antigen testing, though, and ordered 150 million tests from Abbott when the company’s more advanced technology came online. In October, the Associated Press reported that while about half of the country’s testing capacity consisted of antigen tests, the overall reported test numbers didn’t reflect the flood of antigen tests that had made their way to states. In November, The New York Times found the same hole in the data, reporting that state and local public-health officials were on the hunt for rapid-testing facilities that were not disclosing their data.
And that hole doesn’t seem to have gone anywhere. On December 14, during a biweekly CDC call with laboratory representatives to address their issues in dealing with COVID-19, the Department of Health and Human Services said that a majority of the more than 50 million antigen tests that have been distributed to states “do not have test results flowing to HHS.” According to the CDC data, that number is now up to 94.4 million. Data collected by the COVID Tracking Project similarly suggest that states are not reporting antigen-test results. Out of more than 235 million test results reported since June, only about 9 million are clearly reported as antigen-test results. Admittedly, many states still don’t split out separate figures for antigen tests and PCR tests. But even among the states that do, antigen tests make up only about 10 percent of all tests they have reported. Extrapolated nationwide, that would be about 27 million tests, or a bit more than a quarter of the tests the federal government has distributed to date.