The test, if authorized by the Food and Drug Administration, would be the first commercial product to detect the response of a T cell — a type of immune cell — to the virus. Antibodies have dominated the conversation on immunity since the start of the pandemic, but scientists believe that T cells may be just as important in preventing reinfection.

The test was developed by Adaptive Biotechnologies, a company based in Seattle. The company used small blood samples from 1,000 people across 25 metropolitan areas in the United States as well as another 3,500 participants from Europe to create the test, which can detect a recent or past infection of the coronavirus.

The company’s data has not yet been reviewed for publication in a scientific journal, but experts say the work is promising for assessing T cells’ role in the illness caused by the coronavirus.