Fig. 6

Correlations of antibody isotypes and specific antibodies targeting different antigens. The correlations between antibody level of IgM and IgA targeting S or different S domain (a), correlations between IgG and IgA targeting S or different S domain (b), correlations between IgG and IgM targeting S or different S domain (c), correlation between S-IgG and different S-domain-targeting IgG (d), correlation between S-IgA and different S-domain-targeting IgA (e), and correlation between S-IgM and different S-domain-targeting IgM (f). The correlations 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