Reviewed February 25, 2021
A positive test shows that you have antibodies that may have resulted from COVID-19 infection. It could also be a false positive test from a cross-reaction with antibodies from a related coronavirus or other virus. (Numerous other common coronaviruses also cause mild upper respiratory infections.)
Antibodies can appear approximately one week after infection and typically peak four to six weeks after symptoms begin. Most people develop antibodies two to three weeks after infection. Some patients, particularly those with immunocompromising conditions, don't produce a detectible antibody response. How long antibodies remain in the body after COVID-19 infection is not known. Antibodies to most viruses remain detectable for months or even years after infection.
We don't know yet whether antibodies to this virus offer immunity against future infections. More studies will have to be done to determine whether the presence of antibodies means you can't be reinfected – so decisions about returning to work or school should not be based on antibody test results.
Also keep in mind that antibodies are not the only aspect of the body's immune response that protects you against a virus. Certain types of B cells and T cells also provide protection but are hard to measure. In other words, no longer having antibodies to SARS-CoV-2 doesn't necessarily mean that you're no longer protected.