Fig. 6: Immunization with NDV and MVA viral vectors encoding SARS-CoV-2 S protein protects hamsters challenged with SARS-CoV-2.

A Design of the study. Six- to eight-week-old female Golden Syrian hamsters were used. Groups 1-4 (n = 8/group) were vaccinated with either homologous or heterologous prime/boost regimens with NDV-HXP-S and MVA-S(3P). Groups 5 and 6 were vaccinated with empty MVA and NDV viral vectors as negative control. Group 7 was inoculated with PBS as healthy control. NDV viral vector vaccine was administrated via intranasal (IN) route and MVA viral vector vaccine was administrated via intramuscular (IM) route at days 0 and 28. Serum was collected at day 55 (1 day pre-challenge). Vaccination groups 1-6 were challenged with 1 ×105 PFUs of SARS-CoV-2 New York strain at day 56, while group 7 was mock challenged with PBS. Throat swabs were collected at days 1, 3 and 5 post-challenge. A subset of hamsters (n = 4/group) were euthanized at days 2 and 5 post-challenge to harvest lungs lobes (upper right lung lobe and lower right lung lobe) and nasal turbinates. B Body weight change of hamsters. Body weight was monitored for 5 days post-challenge. C Genomic viral RNA copies in throat swabs. Throat swabs were collected in 200 μL of PBS at days 1, 3 and 5 post-challenge and SARS-CoV-2 N genomic copies detected by RT-qPCR. The geometric mean with geometric SD of values from triplicates of each sample for each group are represented. The dotted line represents the LOD, and the dashed line represents the limit of quantification (LOQ). Two-way ANOVA followed by Tukey’s multiple comparisons test: *p < 0.033; **p < 0.002. (D) Viral load in the nasal turbinates. Nasal turbinates were collected from vaccination groups 1-6 and the healthy control group at days 2 and 5 post-challenge and homogenized in 0.5 mL of PBS. Viral titers were measured by plaque assay on Vero-E6 cells. The geometric mean with geometric SD of values (PFUs/mL) of each sample for each group are represented. The dotted line represents the LOD. Two-way ANOVA followed by Tukey’s multiple comparisons test: ****p < 0.0001. E Viral load in the lungs. The upper and lower right lung lobes were collected at days 2 and 5 post-challenge and homogenized in 1 mL of PBS. Viral titers were measured by plaque assay on Vero-E6 cells. The geometric mean with geometric SD of values (PFUs/mL) of each sample for each group are represented. The dotted line represents the LOD. Two-way ANOVA followed by Tukey’s multiple comparisons test: ****p < 0.0001. F Pathology analyses of the left lung lobes. Left lung lobes from vaccination groups collected at day 5 post-challenge were fixed in 4% paraformaldehyde, cut into 5 µm sections and stained with H&E. The slides were evaluated by a pathologist who was blinded to the group information. The scoring system is shown in Supplementary Table 1. The geometric mean with geometric SD of cumulative histopathological lesion scores are represented. The dotted line represents the LOD. Unpaired nonparametric Kruskal-Wallis test: ****p < 0.0001.