Fig. 2.

Neutralization activity of sera from day 21 and day 35 against SARS-CoV-2 PsV. a The NT₅₀s for each mouse at day 21 using SARS-CoV-2 PsV neutralization assay. b The NT₅₀s for each mouse at day 35 using SARS-CoV-2 PsV neutralization assay. c Antisera from mice immunized with 10 µg RBD-Fc inhibited hACE2 binding to SARS-CoV-2 RBD. Data shown are means ± s.e.m. from six samples. d Detection of SARS-CoV-2 N protein expression in cells treated with pooled sera from mice immunized with 10 µg RBD-Fc using immunofluorescence assay. e Detection of SARS-CoV-2 virus titer in the cell supernatant using RT-qPCR assay. Data shown are means ± s.e.m. from triplicate samples. f The immunization and challenge strategy of hACE2 mice. g The virus titers in the lungs of hACE2 mice. *P < 0.05; **P < 0.01; ***P < 0.001. All experiments were repeated at least twice