Figure 3.

Immunogenicity of the F8 and 8X vaccines in mice. Mice were immunized with F8 and 8X vaccines at day 0 and booster at day 7. Aluminum hydroxide at a concentration of 0.5 mg/ml in PBS was used as the negative control. The S protein content was used to quantify the vaccine dose. High dose: 135 ng of S protein. Low dose: 27 ng of S protein. Each group had six mice. Serum was collected at 1, 2, 3, 4, 5, and 6 weeks post booster vaccination. (A) SARS-CoV-2-specific IgG antibody titers were determined by ELISA. *Significant difference between the two groups (p < 0.05). (B) Serum samples at 1, 3, and 6 weeks post the booster vaccination were obtained, and the neutralizing antibody titer was measured by the plaque reduction neutralization test. Serum dilutions leading to 50% plaque reductions (PRNT₅₀) were calculated as titers. *Significant difference between the two groups (p < 0.05).