Fig. 7

Correlations of specific antibody responses and illness day. The correlations between days after symptom onset and IgG titers (a), IgA levels (b), IgM levels (c), and IgG subclasses (d) were determined by the spearman rank method, P values < 0.05 and r > 0.3 or < − 0.3 were considered statistically significant. Red dots, r1 and P1 represent sample from severe cases; blue dots, r2 and P2 represent samples from non-severe cases