Fig. 3

Humoral immune responses were assessed in immunized mice. A The experimental timeline and sample collection protocol for vaccinating BALB/c mice. B, C Serum specimens were determined for SARS-CoV-2 S1 and N protein-specific IgG, IgG2a, and IgG1 endpoint titers by ELISA. D, E Bar chart of logarithm values of the ratio IgG2a: IgG1 of S1 and N protein. Data are reported as mean ± SD (n = 8). Comparisons were performed by one-way ANOVA with the Bonferroni correction in SPSS 21.0. ***p-value < 0.001, **p-value < 0.01, *p-value < 0.05, ^nsp-value > 0.05. Data were combined from three parallel replicates per sample. Colored symbols indicated individual animals’ values. F Antibodies that block the hACE2 receptor in pooled serum (n = 8/group) collected at 21st days post-boost vaccination. G SARS-CoV-2 spike pseudovirus 50% serum neutralizing antibody titers (pVNT50) in pooled serum (n = 8/group) collected from (F). Bars indicate the mean ± SD of three parallel replicate assays per sample