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Serological assays for COVID-19 virus antibody for the patient and her 33 colleagues (shown as close contacts). Antibody titers were measured with commercial chemiluminescence kits for COVID-19 virus. Cutoff index (COI) values are indicated on the Y-axis. (A) Total antibody (Total Ab); (B) Immunoglobulin G (IgG); (C) Immunoglobin M (IgM).
