The Promise and Peril of Antibody Testing for COVID-19 | Infectious Diseases | JAMA | JAMA Network

In the first such community-wide campaign in the US, the San Miguel County Department of Health offered the voluntary screening to most of the area’s 8000 residents over 2 weeks. Just 8 of the 986 individuals tested on March 26 and 27 were positive for SARS-CoV-2 antibodies. Another 23 were borderline, suggesting that they’d recently been exposed to the virus and were just starting to make antibodies against it. But those were early days. The screenings, paid for by test manufacturer United Biomedical Inc and the county, eventually would be repeated to see how much things had changed.

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.

Serologic antibody tests not only can confirm suspected cases after the fact, they can also reveal who was infected and didn’t know it. Up to a quarter of people with SARS-CoV-2 infection may unwittingly spread the virus because they have mild or no symptoms.

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.

Via: The Promise and Peril of Antibody Testing for COVID-19 | Infectious Diseases | JAMA | JAMA Network