CNN
Antibody tests used to determine if people have been infected in the past with Covid-19 might be wrong up to half the time, the CDC said in new guidance posted on its website. Antibody tests, often called serologic tests, look for evidence of an immune response to infection. "Antibodies in some persons can be detected within the first week of illness onset," the CDC says. They are not accurate enough to use to make important policy decisions, the CDC said.