Fig. 3

d16 as a live attenuated vaccine to alleviate disease in hamsters infected with SARS-CoV-2. A Vaccination and viral challenge scheme for the hamster model. Hamsters were intranasally inoculated with 10⁵ PFU (in 50 µl) of recombinant WT or d16 SARS-CoV-2 on day 0. Serum samples were collected from each group on days 0, 14 and 28 for ELISA and neutralization tests. On day 29, the immunized hamsters were challenged with 10⁵ PFU (in 50 µl) of clinical isolate HK-13 of SARS-CoV-2. Respiratory tissues (tracheae and lungs) and the nasal wash were collected on day 33, and each respective viral load was detected by a plaque assay. Body weights were recorded daily from day 29 to day 43 after viral challenge. B Antibody responses in hamsters infected with WT SARS-CoV-2 or immunized with d16 SARS-CoV-2 were measured by ELISA to assess RBD-specific antibodies. C The cross-neutralization capability of infected/immunized hamster sera (1:10 dilution) was examined using the SARS-CoV-2 sVNT assay. The dotted line represents the assay cutoff at 30% inhibition. D SARS-CoV-2 neutralization tests to examine the neutralization ability of hamster sera collected from different groups. E Body weight changes of HK-13-infected hamsters (n = 5) vaccinated with d16 viruses or PBS. The WT virus-reinfected group served as a control. F Viral titer determination by a plaque assay for the nasal wash, tracheal tissues and lung tissues of HK-13-challenged hamsters in the WT, d16 or PBS group at 4 dpi (n = 4/group). LOD limit of detection. G Hamster cohousing scheme. Briefly, d16- or sham-vaccinated hamsters (n = 4/group) were infected with SARS-CoV-2 on day 29 post-vaccination and subsequently cohoused with immunologically naïve hamsters for 8 h at 2 dpi, followed by separation and viral load analysis of the recipient hamsters on day 4 post-cohousing. H Viral loads in the nasal wash and lung tissues of recipient hamsters at 4 days post-cohousing. LOD limit of detection. I Histopathological changes in the lungs of SARS-CoV-2-challenged hamsters in the WT, d16 or PBS group at 4 dpi. Representative sections were stained with H&E. Scale bars, 200 μm. J Transcript levels of representative proinflammatory chemokines and cytokines in lung tissue homogenates from the WT, d16 and PBS groups, as measured by RT–qPCR. The results are shown in arbitrary units as the mean ± SEM. Statistical analyses were performed with Student’s t-test (*P < 0.05; **P < 0.01; ***P < 0.001).