Plasma antibody analysis from mRNA-vaccinated human cohorts. (A) Schematic of sample collection. Plasma and PBMCs were collected from 2 to 3 wk after the first vaccination (pre-2nd, n = 12), 1–3 wk after the second vaccination (post-2nd, n = 12), ∼9 mo after the second vaccination (pre-3rd, n = 26), and 1–2 wk after the third vaccination (post-3rd, n = 26). (B) Plasma anti–RBD-W or RBD-O IgG titer quantified by ELISA and expressed as relative quantity of EY6A antibody. (C) Plasma neutralization activity against VSV pseudotyped with SARS-CoV-2 Wuhan or Omicron BA.1 spike protein expressed as NT50 values. (B and C) Experiments were performed in duplicate. Lines connect the longitudinal samples. *, P < 0.05; ***, P < 0.001; ****, P < 0.0001 by Wilcoxon test.