Figure 3.
Longitudinal analysis of plasma antibody titers
Anti-RBD (A–C) and anti-S (D–F) IgM, IgA, and IgG antibodies in paired samples from 42 COVID-19 patients over 15 months. For anti-RBD (C) and anti-S (F) IgG antibodies, further comparisons were made between paired samples (n = 11) at two time points ranging from 6 to 15 months (TP1: 181–300 and TP2: 301–452 days after symptoms onset; right panel). Symbols represent individual subjects; horizontal black lines indicate the median and 95% CI. The antibody decay curves (in black) and half-lives (t1/2) were estimated by a one-phase exponential decay model. The dashed red line indicates the cutoff value for elevated anti-S and anti-RBD antibody titers (2.5 and 8.4 AU/mL for IgM, 0.5 and 0.08 AU/mL for IgA, and 0.03 and 14.81 AU/mL for IgG, respectively, giving a specificity of 96% for IgM, 99% for IgA, and 97% for IgG). The cutoff-value is not visible in some graphs because it is very close to the X axis. Wilcoxon signed-rank test. See also Figure S1.