Fig. 4

Protection of 3Ro-NC-immunized hACE2 mice against SARS-CoV-2 variant Omicron infection. A Diagrammatic scheme of the immunization and virus challenge (n = 6–8 mice per group). B RBD-specific serum IgG, salivary IgA and vaginal IgA after the 3rd immunization. C Neutralization antibody titers against authentic SARS-CoV-2 Omicron BA.1 in serum after the 3rd immunization. D Correlation of NT₅₀ against Omicron BA.1 with the Omicron BA.1 RBD-specific serum IgG. E qPCR-tested RNA copies of SARS-CoV-2 RBD and plaque assay of infectious virus in the lung at 3 days post-infection. F Hematoxylin and eosin (H&E) staining of the lung sections (scale bars, 100 µm). Infiltrations of immunocytes are labeled by arrows. G Pathological scores according to the H&E-stained sections. H Infiltration score of immunocyte aggregation around bronchioles, pulmonary vessels and interstitial pneumonia. I qPCR was used to test RNA copies of SARS-CoV-2 RBD in turbinates at 3 days post-infection. J Correlation of RNA copies in the lung and turbinate. K, L Correlation of RNA copies in the lung and turbinate with Omicron BA.1 RBD-specific serum IgG and salivary IgA. The 95% confidence interval is indicated by dotted lines. Groups were compared using one-way ANOVA. *P < 0.05; **P < 0.01; ***P < 0.001; ns nonsignificant. LOD limit of detection