Figure 2.

The bivalent D614G/B.1.351_RBD-NP vaccine protects against D614G and (B)1.351 variant infection in hACE2 mice

(A) Schematic of hACE2 mouse vaccination. Five mice in each group were primer-boost-vaccinated with the bivalent D614G/B.1.351_RBD-NP on day 0 and day 28. Mice were challenged with authentic SARS-CoV-2 (D614G/B.1.351) on day 56. All mice were bled and euthanized 5 days after challenge.

(B) D614G_RBD-specific and B.1.351_RBD-specific IgG antibody titers of serum were determined using ELISA by serial dilution and are represented as the reciprocal of the endpoint serum dilution.

(C) The serum of each mouse was 10-fold serially diluted and incubated with 500 focus-forming units (ffu) of authentic SARS-CoV-2 (D614G/B.1.351), followed by incubation with Vero E6 cells. The FRNT spots of each well were counted. FRNT50 of nAbs of each vaccine group was determined by FRNT and is represented as IC₅₀.

(D and E) Viral RNA copies in the lungs and trachea of each mouse were determined by qRT-PCR and plotted as log₁₀ copies per milliliter. A dotted line indicates the limit of detection (LOD).

(F and G) H&E staining of the lungs of each mouse.

(H and I) Immunohistochemistry (IHC) against N proteins was evaluated in the lungs of each mouse. Scale bars (F–I) represent 50 μm. Each dot represents serum from one animal.

Experiments were conducted independently in triplicate. Data are represented as mean ± SD. Adjusted p values were calculated by one-way ANOVA with Tukey’s multiple comparisons test. Significant differences between groups linked by horizontal lines are indicated by asterisks. ^∗p < 0.05, ^∗∗p < 0.01, ^∗∗∗p < 0.001.