Figure 2. IgM antibody responses to SARS-CoV-2 in vaccinated 2-year convalescents.
IgM antibody levels were measured by MCLIA and ELISA in healthy individuals after being vaccinated (HC-Vac, green, n=35) or unvaccinated (HC-Unvac, blue, n=26), and in COVID-19 convalescents following at 6 months (6m, orange, n=23), 1 year (1Y, green, n=23) and 2 years with vaccination (2Y-Vac, red, n=51). A-B, Anti-SARS-CoV-2 IgM antibody titers determined by ELISA (A) or MCLIA (B). C-D, The longitudinally dynamic changes of IgM levels in convalescents at 6 months, 1 year, and 2 years in the same individuals after symptoms onset, using ELISA (C, n=23) or MCLIA (D, n=18). E-F, Correlation of IgM titers and different disease severity in 51 vaccinated 2-year convalescents (2Y-Vac), including Asym-Mild (Asymptomatic and Mild, red, n=25) and Mod-Sev (Moderate and Severe, dark green, n=26). Black bars denote median responses. Each multi-colored dot or connective line indicates one individual. The dotted lines reflect the cut-off values for positive antibody titers. Significant differences in antibody titers were tested using a Mann-Whitney U-test (A-B, E-F). A Wilcoxon matched-pairs signed rank test was used to compare IgM antibody titers at three time points (C-D). * p < 0.05, ** p < 0.01, *** p < 0.001.