Fig. 1: Anti-IgG ELISA binding titers against ancestral (Wuhan WT) or Omicron BA.1 RBD.

a Hospitalized COVID-19 patients (37 subjects); b SARS-CoV-2-naïve vaccinees immunized with two doses of homologous mRNA vaccine (49 subjects); c previously infected subjects who had received a double dose of homologous mRNA vaccine (23 subjects); d vaccinees boosted with a third dose of mRNA after completion of primary double-dose vaccination with mRNA-based (homologous) vaccine (44 subjects); e vaccinees boosted with a third dose of mRNA after completion of primary double-dose vaccination with adenovirus-based (heterologous) vaccination (35 subjects); f ELISA Geometric mean titers (ELISA GMT) for each cohort and for ancestral virus and Omicron BA.1 variant. Y axis shows the reciprocal of serum dilutions (Rec. serum dilution). Data points show individual serum ELISA titers (average of two replicates). The ELISA titer is represented as the reciprocal of the highest serum dilution able to provide an absorbance value greater than the cut-off value. ELISA GMTs for each cohort are shown. Error bars indicate the GMT of the group ± standard deviation. Fold-changes in GMT are reported above histograms. P values were calculated by means of the Mann–Whitney U-test. Horizontal dashed line represents the Lower Limit of Quantification (LLOQ) of the assay. Different LLOQ were set according to the expected response of each cohort (COVID-19 patients LLOQ: 500; 2x mRNA vaccine LLOQ: 400; N positives plus 2x mRNA vaccines LLOQ: 800; 3x mRNA vaccine LLOQ = 800, 2x adenoviral plus 1xmRNA vaccine LLOQ: 800).