Humoral immune responses in immunized BALB/c mice (n = 5/group) and convalescent patient sera (N = 3). A and B) Five groups of BALB/c mice were immunized with the indicated doses of PRAK-03202 (n = 5/group). PRAK-03202-specific IgG antibody titers were analyzed by ELISA in mice (A) and in (B) healthy and convalescent patient sera. Bars represent the mean titer, with standard deviation indicated. C) Bar chart depicting the NP of PRAK-03202 in immunized mice relative to the NP of convalescent patients, which was taken as reference. Corrected NP (%) = (average NP of sera samples of immunized mice/average NP of sera samples from convalescent patients) X100. ∗Indicates statistically significant difference (P < 0.05). D) Vero E6 cells were infected with the 30 PFU of wild type SARS-CoV-2 and serum mixture at the indicated dilutions. PRNT50 titer was plotted for each group of immunized mice. E) Antigen-specific -fold changes in IgG responses (spike, envelope, and membrane proteins) of PRAK-03202 were measured by ELISA in immunized mice. PRAK-03202 was incubated with 0.25 μg of purified spike, envelope, and membrane protein-coated 96-well plates. The plates were read at 450/630 nm using an ELISA plate reader. Error bars indicate SEM.