Fig. 4

Correlation analysis between serum antibody titers and the year of birth (the history of smallpox vaccination). Statistical comparison of serum antibody titers against A35R (A, purple), B6R (B, blue), A29L (C, green), and M1R (D, red) between individuals born before and after 1980 (Left). Means with standard deviations are shown. The p values were calculated by Mann Whitney t-test; n.s., p > 0.05; *, p < 0.05. Correlations were analyzed between serum ELISA AUC values and donors’ ages, and evaluated by Spearman’s rank correlation method (Right). The percentages of individuals with high levels of serum binding activity (AUC > 24) are labeled for donors born before and after 1980 (43 years old), respectively. In 1980, smallpox vaccination halted in China