Fig. 4: Study design, weight evolution and humoral immune responses of SARS-CoV-2 inoculated golden Syrian hamsters (GSH).

a Overview of the immunisation and inoculation strategies in geriatric GSH. Animals received two immunisation doses, three weeks apart (syringe symbol); blood drops indicate the collection of biological samples; GSH were inoculated either 20 days or 4 months after the booster dose. b–i Kinetics of the humoral immune response in geriatric GSH: anti-S IgG and anti-RBD IgG in both the short-term and long-term groups before (b–e) and after (f, g) inoculation; neutralising activity against SARS-CoV-2 WH1 (h) and Omicron BA.1 (i) variant after inoculation (pseudovirus neutralisation assay). Differences between groups were determined using the Kruskal-Wallis test, and longitudinally using the Friedman test. Post-hoc tests were performed using the corresponding Conover’s test. P values < 0.05 were considered significant; *p value < 0.05; **p value < 0.01; ***p value < 0.001. j 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.