The humoral immune response induced by SARS-CoV-2.

(A) IgG seropositivity (optical density [OD] ratio ≥ 1.1) analysis by sampling day: D0, day of enrollment; D3, the third day after enrollment; D7, 7 days after enrollment. Dashed columns represent the patients who received convalescent plasma (CP) at enrollment (n = 26 samples available on day 0, n = 26 on day 3, and n = 23 on day 7); white columns represent the patients from the deferred plasma group who did not receive plasma (n = 20 samples available on day 0, n = 20 on day 3, and n = 12 on day 7). Above each column, the percentage of seropositivity is indicated. (B) IgG seroconversion was considered to have occurred if a patient had a negative sample at 1:100 dilution at baseline but increased to any positive dilution after 72 hours or 7 days, or if a 4-fold increase in endpoint dilution titer from baseline was reached. Dashed columns represent patients who received CP; white columns represent patients from the deferred plasma group who did not receive plasma. Above each column, the percentage of seroconversion is indicated. (C) Neutralizing antibody (NAb) titer measured by 50% inhibitory dose (ID50) quantified at D0. The total number of patients reaching every dilution titer interval is indicated above each column. *ID50 titer ≤ 1:159 or no neutralization observed. (D) NAb titers showed by days since COVID-19 symptom onset. Each column represents the number of days after onset of symptoms; above each column are the number of individuals. Summary statistics above represent the number of individuals with NAb titers ≥ 1:160 from 2 groups: those enrolled in the first 5 days since symptom onset and those enrolled 6 or 7 days since symptom onset. *ID50 titer ≤ 1:159 or no neutralization observed.