Antibody tests are designed to have low false positives, not low false negatives. And blood samples have found that a proportion of samples have t-cell immune

Antibody tests are designed to have low false positives, not low false negatives. And blood samples have found that a proportion of samples have t-cell immune responses to sars-cov-2 without antibodies, possibly with no exposure to sars-cov-2 specifically. Specific antibody levels drop after a few months. Therefore, might be impossible to establish if someone was exposed or what level of immunity.