The first wave of Covid-19 tests asked, Do you have the SARS-CoV-2 virus right now? But as the world starts to eye an exit from lockdown, it needs tests that can answer a different question: Did you have the virus in the past? If so, a person should have antibodies: proteins in the blood that will recognize and grab onto the virus if it comes back, and — hopefully — block reinfection.
Testing for antibodies could answer key questions about the virus, helping epidemiologists track exposures and potentially leading to the issuing of “immunity passports” for people who’ve beaten back the infection and can return to work. “I think you’re going to see [antibody testing] explode,” says allergist Mitchell Grayson, chief of allergy and immunology at Nationwide Children’s Hospital and Ohio State University in Columbus.
But even though it’s likely that someone carrying antibodies to SARS-CoV-2 would be protected from repeat infection, scientists don’t yet know that. The World Health Organization recently warned against issuing immunity certificates based on antibody tests for that reason. And the tests themselves are plagued with high rates of inaccuracy. The United Kingdom, for example, paid $20 million for antibody tests that Oxford University later deemed too insensitive to detect antibodies in all but the sickest patients.
In the United States, eight organizations had received emergency use authorization from the Food and Drug Administration for antibody tests, as of April 30. But the FDA announced in March that test makers could sell Covid-19 diagnostics as soon as they’re satisfied with their own test and have notified the FDA, before the agency has reviewed their data. Dozens of tests have come out under these guidelines.
Here’s some of what we know about antibody tests for Covid-19, and what scientists still need to find out.
