Figure 2: Sustained neutralizing antibody responses against Beta and Omicron BA.1 variants upon MCMV^S immunization.

(A) Schematic image of the experimental setup and legend. Mice were challenged with 6×10⁴ PFU of SARS-CoV-2 in all settings. Created with BioRender.com. (B, C) Mice were challenged at 6 weeks after immunization. Relative body mass (B) and clinical scores (C) were monitored daily upon challenge with the Beta variant. (D-F) Mice were challenged with SARS-CoV-2 Beta 20 weeks after immunization. (D) Percentage of body mass, (E) daily clinical scores and (F) survival kinetics of challenged mice represented as the percentage of mice reaching the humane end point due to a high clinical score. The threshold resulting in this humane end-point is indicated by the red dotted line in panel (E). (G) Infectious virus titers in lungs of SARS-CoV-2 Beta-challenged mice 6 weeks (left) and 20 weeks (right) post immunization. (H) Relative viral RNA loads in lungs of SARS-CoV-2 Beta-challenged mice normalized to GAPDH. (J) Pseudovirus serum neutralization titers resulting in a 50% reduction of SARS-CoV-2 infection (PVNT₅₀). PVNT₅₀ at 6 weeks (n=8; left) and 20 weeks (n=24; right) post-vaccination against the Index (Wuhan), Beta and Omicron BA.1 variants. Titers were assessed seven days before SARS-CoV-2 challenge. Dot plots representing the same mice are connected by lines. Solid horizontal lines show the median and the dotted line indicates the detection limit. (J) Correlation of Infectious virus titers in lungs and PVNT50 against the Index strain of SARS-CoV-2 Beta-challenged mice after 20 weeks post immunization. (K) Relative viral RNA loads in lungs of SARS-CoV-2 Omicron BA.1-challenged mice normalized to GAPDH. Statistical significance for was calculated using Welch’s t test (two-tailed) (* p < 0.05, ** p <0.01, *** p < 0.001).