The U.S. Centers for Disease Control and Prevention recently started testing for coronavirus exposure in asymptomatic people using serological tests — finger-prick blood tests to see if people have recovered from the virus by identifying antibodies in their blood. This differs from the nasal swab PCR (polymerase chain reaction) tests being used at drive-through sites across the Philadelphia region to diagnose those who currently have the virus.

Serological testing could identify people, most notably health-care workers, who could safely go back to work. It also could identify those who don’t have immunity so they can be first in line for a vaccine, which won’t be available for at least another year.

Last week, the U.S. Food and Drug Administration issued its first emergency use authorization for a serological test that can be done in certified labs. Other health-care companies are seeking government clearance for home kits that allow users to submit a scanned picture of their blood to doctors via their phones.

“We definitely want to know if people have antibodies to provide immunity, especially as we’re waiting for a vaccine,” said Kathleen Bachynski, an assistant professor in public health at Muhlenberg College. “That information is going to be crucial to inform our understanding of public health risk and the course of the pandemic."

But before you search out serological testing so you can go back to work or start attending public gatherings again, know that there are many caveats to this type of test.

Infectious disease experts have cautioned that taking a serological test immediately after an infection may yield a false negative result, because the immune system has not had time to develop antibodies. Most people become positive for antibodies about 14 days after they start experiencing symptoms. People can also test positive if they have antibodies against a different coronavirus, like those that cause the common cold.

And while the tests can identify whether antibodies exist, there is no way to know how well those antibodies are working, health officials say. It’s also unclear whether an immune response can protect people like health-care workers who are exposed to larger “doses” of the virus.

Some countries, like Germany, are considering issuing “passes” to people who test positive for COVID-19 antibodies, which will allow them to go back to work. But those steps may be premature, as researchers don’t know how long immunity lasts, and can’t use serological tests to find out whether people who test positive for antibodies are still contagious.

“We still have a lot to learn about how immunity works and how accurate these tests are,” Bachynski said.

Given the unknowns, experts say the best approach, regardless of whether you think you’ve been infected, is to follow social distancing measures to avoid getting infected until a vaccine is approved and deployed.

“We are not yet at a point where we can confidently use this test for mass screening or to determine which members of the general public are or aren’t immune," Bachynski said. "In the meantime, we must continue social distancing measures and hand-washing as the best ways to reduce the spread of the virus.”