"Unlike polymerase chain reaction (PCR) tests—also referred to as molecular or nucleic acid–based tests—antibody tests aren’t intended to identify active SARS-CoV-2 infections. Instead of detecting viral genetic material in throat or nasal swabs, antibody tests reveal markers of immune response—the IgM and IgG antibodies that for most people show up in blood more than a week after they start to feel sick, when symptoms may already be waning.

Implications for the health care workforce could be substantial, microbiologist Florian Krammer, PhD, of Mount Sinai’s Icahn School of Medicine, said in an interview. “If we find serologically that you are immune, it’s very unlikely that you can get reinfected, which means you can’t pass the virus on to your colleagues or to other patients. And I think it also gives a peace of mind if you have to work with COVID-19 patients to know that you’re probably immune to the infection,” he explained.

Antibody tests are ramping up quickly, with a growing list of commercial kits and test protocols from academic researchers including Krammer’s team and a Dutch team coming online in recent days and weeks. Scientists said the tests will be critical in the weeks and months ahead, when they may be used for disease surveillance, therapeutics, return-to-work screenings, and more. But the tests must be deployed appropriately, they added, and with an acknowledgment of unanswered questions."