The Atlantic Antibody tests for the coronavirus have just one scientifically sanctioned job in the clinic. Designed to detect a delayed immune response to the virus, they can help patients determine whether they were once infected—effectively, a retroactive diagnosis. That’s not how a lot of antibody tests are being used. Across the country, people have flocked to test sites to determine whether they are “immune” to the coronavirus, or even to obtain results that could green-light them to board an international flight. Now they are taking these tests to check whether the vaccine they received actually took. Some experts are even debating whether the tests could serve as a screening tool to identify candidates who might be eligible to skip their second COVID-19 shot.