Fig. 3. Humoral and B cell responses to COVID-19 RNA vaccination.

Responses to COVID-19 RNA vaccines in previously infected study subjects and non-infected comparators were determined. Receptor Binding Domain (RBD)-specific IgG antibody binding, plasma neutralizing activity, and B cell frequencies were assessed as in Fig. 1, 2. Infection (INF) and vaccination (VAC) status is indicated by (+) and (−) signs. (A,B) Titers of RBD-specific IgG by ELISA; (C,D) NT50 determinations in neutralization assays. Pre-vaccination samples of previously infected subjects in panels (A,C) were those collected last prior to vaccination to determine effect of vaccination; in panels (B,D) were those collected first (< 2 months) post SARS-CoV-2 diagnosis to compare responses to recent infection and recent vaccination. (E) Frequency of RBD-specific memory B cells (RBD⁺MBC). We used only one dataset for pre-vaccination infected subjects for RBD⁺MBC, because these cells do not vary between the <2 and >5 data points. (F) Frequency of total double-negative memory B cells (DNM, CD27⁻IgD⁻). RBD-specific DNM frequency showed the same downward trend post-vaccination (p = 0.05). In all panels, data are shown as scatter plots; each circle represents one study subject; the solid black lines represent the median and interquartile range. Statistical analysis was performed either with Mann-Whitney U-test for unpaired data or Wilcoxon matched-pairs signed rank test for paired samples; * p < 0.05, ** p < 0.01.