Fig. 5.

SARS-CoV-2 live virus neutralization ability of sera from mice immunized with GNP-conjugated vaccine candidates. Sera (Day 61) from all groups of immunized mice were evaluated for live virus neutralization ability against SARS-CoV-2 WT, WI, and delta variants. Sera (5× diluted, starting from 1:25) were separately incubated with WT, WI, and delta viruses at 10⁴ PFU for 1 h. Next, the virus-sera mix was added to the cells and incubated for 24 h. Then cells were fixed and permeabilized and stained with the combination of anti-SARS-CoV-2 spike protein antibodies (rabbit mAb) and Alexa Fluor 488 goat anti-rabbit as primary and secondary antibodies, respectively. The nuclei were stained using Hoechst 33342 and plates were read using Operetta Imager. The percent neutralization was calculated based on the differential intensity of the fluorescence.