Fig. 3

S1-specific total IgG and IgG subclasses in older adults with and without SARS-CoV-2 infection prior to the start of COVID-19 vaccination. SARS-CoV-2 spike S1-specific total IgG, IgG1, IgG2, IgG3 and IgG4 concentrations following the fifth mRNA vaccination were measured in serum by multiplex immunoassay for older adults with (n = 4) and without (n = 50) SARS-CoV-2 infection prior to the start of vaccination. Dotted lines indicate the cut-off for seropositivity. Differences between groups were assessed using a non-parametric Wilcoxon signed rank test with Bonferroni’s correction for multiple testing. * P < 0.05. AU, arbitrary units; BAU, binding antibody units