Fig. 2.

(A) Vaccination. blood collection, and challenge regimen in K18-hACE2 mice challenge study. Mice were divided into 3 groups (n = 12): the control and Baiya SARS-CoV-2 Vax 2 (dose 5, 10 µg of RBD-Fc adjuvanted with 1 µg of 3 M-052-AF plus 50 µg Al content of alum) groups. The mice were intramuscularly injected on day 0 and 21, and blood was collected on day 0, 14, and 35. On day 35, the immunized mice were intranasally infected with SARS-CoV-2. Half number of mice in each group (n = 6) were humanely euthanized on four days after SARS-CoV-2 challenge and the other half were euthanized on 6 days after SARS-CoV-2 challenge. The organs were collected 4 or 6 days post-infection. (B) The percent body weight change of challenged mice after infection. The data are presented as mean ± SEM. Mixed-effects analysis, Tukey test, was used (*: p < 0.05, ***: p < 0.001, ****: p < 0.0001). (C) RBD-specific total IgG determined by ELISA and (D) 50 % neutralizing antibody (MN50) titer against SARS-CoV-2 clinical isolate as determined in a live virus microneutralization assay. Dotted lines indicate the assay limit of quantitation. The data are presented as geometric mean titers with 95 % confidence intervals. Two-way ANOVA, Tukey test, was used (*: p < 0.05, **: p < 0.01, ***: p < 0.001, ****: p < 0.0001). (D) Values smaller than the limit of detection (LOD) are plotted as 0.5*LOD.