Fig. 4: Intranasal vaccination with AdC68-HATRBD protects K18-hACE2 mice from BA.5.2 challenge.

a Scheme of vaccination and challenge. K18-hACE2 mice (n = 6 per group) were immunized intranasally with 5 × 10⁷ IFU of AdC68-HATRBD using prime-only or prime-boost regimen. The control group received a placebo (PBS). At 8 weeks post-vaccination, mice were challenged with BA.5.2 and monitored for clinical signs and weight loss. Mouse serum was obtained to test for the neutralizing activity against BA.5.2 1 day prior to challenge. At 5 day post-infection, mice were euthanized, and tracheas and lung tissues were collected. b, c Percent weight loss (b) and percent survival (c) over 5 days post-infection. d Serum BA.5.2 neutralizing antibody titers prior to challenge. The red dashed line represents the lower limit of detection. e, f SARS-CoV-2 viral burden in the lungs and tracheas, measured by copies of the viral gRNA (e) and sgRNA (f). g Hematoxylin and eosin staining of lung sections from K18-hACE2 mice at 5 day post-infection. h Histopathological severity scoring was evaluated according to the pathological changes outlined in the methods section. i Spearman’s correlations of FRNT₅₀ titers with viral gRNA copies (left), viral SgRNA copies (middle), and lung pathology scores (right). Each dot represents one animal. Values of geometric mean titer (GMT) are displayed in (d). Data are represented as GMT ± SD (d) or mean ± SEM (b, c, e, f, and h) and analyzed by one-way ANOVA with Tukey correction. In (b), asterisks (*) and pound signs (#) indicate the statistical significance level of control group compared with prime-only group and prime-only group, respectively, at 5 dpi. *^,#P ≤ 0.05, **P ≤ 0.01, ***P ≤ 0.001, and ****P ≤ 0.0001. Scale bar, 50 μm.