Fig. 1: Study design, survivability, weight evolution and humoral immune responses of SARS-CoV-2 inoculated K18-hACE2 geriatric mice.

a Overview of the immunisation and inoculation strategy in K18-hACE2 geriatric mice. Animals received two immunisation doses, three weeks apart (syringe symbol); blood drops indicate the collection of biological samples, SARS-CoV-2 D614G inoculation/challenge two weeks after the booster dose. Kinetics of the humoral immune response in K18-hACE2 geriatric mice: anti-S IgG (b), anti-RBD IgG (c); neutralising activity against SARS-CoV-2 WH1 (d) and Omicron BA.1 (e) variants after viral challenge (pseudovirus neutralisation assay). Differences between groups were determined using the Kruskal-Wallis test. P values < 0.05 were considered significant: *. f Body weight was recorded daily after inoculation. Differences between groups were assessed by mixed two-way ANOVA followed by Tukey’s multiple comparisons test, using the infected control or the uninfected control group as a reference; statistically significant differences are indicated by the * or # symbol, respectively, depicted with the colour of the group being different. Mean and standard deviation are shown for each experimental group. P values < 0.05 were considered significant; *, #: p value < 0.05; **, ##: p value < 0.005; ***, ###: p value < 0.001. g Kaplan-Meier plot showing the survival rate after inoculation.