Maintenance of SARS-CoV-2-specific antibodies in convalescent COVID-19 subjects. (A) Measurement of neutralizing antibody titers in six convalescent subjects by a pseudovirus-based assay. c#9 is indicated by an arrow. (B) Titration of individual serum samples for detection of anti-virus Ig. (C) Data from the same experiments as (B) are presented as area under the curve (AUC). (D) Levels of IgG1 antibody reactive with recombinant NP and S-RBD of convalescent subjects at their first (2 weeks) and second (4–5 months) post discharge visits. The experiment was done in duplicate. Data in C are presented as mean±SEM. NP, nucleocapsid protein. S-RBD, receptor binding domain of spike protein. HD, healthy donor. c, convalescent subject; AUC, area under the curve. * P<0.05, ** P<0.01, ns., not significant.