Scientists believe millions of people have been infected with the coronavirus and recovered without ever knowing for certain whether they had it. Antibody tests have been used to spot past infections, but researchers say a new test detecting immune cells called "T cells" could be far more effective, the New York Times reports. Seattle-based company Adaptive Biotechnologies says that in research using samples from Vo, Italy, where the entire town was tested in March, its "T-Detect" test was able to correctly identify 97% of those who had tested positive, while a commercial antibody test only identified 77%. Experts say T cells are a more reliable indicator of past infection than antibodies, which wane after the body fights off the infection and can be undetectable after a few months.
"The source of the antibodies—the factory that makes them—dies off within a few months," while T cells tend to stay a lot longer, Akiko Iwasaki, an immunologist at the Yale School of Medicine, tells CNN. "For other viruses they've been shown to persist for years. For this virus we don't know how long they last, but we would expect for a couple of years at least," she said. T cells for individual viruses are much trickier to detect than antibodies, though Adaptive Biotechnologies, which was developing a Lyme disease test when the pandemic hit, says its technology was able to successfully spot evidence of infection by identifying proteins on the cells' surface known as T-cell receptors. The company hopes to launch the test commercially by the end of this month. (Read more coronavirus stories.)