Qualitative assessment of SARS-CoV-2-specific antibody avidity by lateral flow immunochromatographic IgG/IgM antibody assay

Qualitative assessment of SARS-CoV-2-specific antibody avidity was conducted using an urea (6M) dissociation test performed on a lateral flow immunochromatographic IgG/IgM device. We included a total of 76 serum specimens collected from 57 COVID-19 patients, of which 39 tested positive for both IgG and IgM and 37 only for IgG. Sera losing IgG reactivity after urea treatment (n=28) were drawn significantly earlier (P=0.04) after onset of symptoms than those which preserved it (n=48). This assay may be helpful to estimate the time of acquisition of infection in patients with mild to severe COVID-19.