Figure 4: Aged MCMV^S immunized mice show full and long-lasting protection against heterologous SARS-CoV-2 challenge.

(A) Legend of experimental cohorts. Created with BioRender.com. (B-G) Mice were challenged with 2×10³ PFU of SARS-CoV-2 (B-D) Delta or (E-G) Omicron BA.1 12 weeks after immunization. (B, E) Percentage of initial body mass and (C, F) daily clinical scores upon challenge are shown. The red dotted line indicates the threshold in score resulting in a humane end-point. (D, G) Survival kinetics of challenged mice representing the Percentage [%] of mice reaching a humane end point. A log-rank (Mantel-cox) test was used for the statistical analysis. (H) SARS-CoV-2 N gene copy numbers as copy number/ng RNA Log10 at 5 d p.i. with SARS-CoV-2 Delta (top) or Omicron BA.1 (bottom) in lung homogenates (I-J) Infectious virus titers in (I) lungs and (J) brains of SARS-CoV-2 Delta-(top) or Omicron BA.1 (bottom) challenged mice. Statistical significance was calculated using Welch’s t test (two-tailed) (* p < 0.05, ** p <0.01, *** p < 0.001).