Fig. 3: Inactivated NDV-HXP-S induces protective antibody response in hamsters.

a Design of the study. Eighteen-to-twenty-week-old female Golden Syrian hamsters were used. Groups 1–3 (n = 8) were vaccinated with 5 µg of NDV-HXP-S without adjuvants, with CpG 1018 and AddaVax, respectively. Group 4 (n = 8) was vaccinated with 5 µg of WT NDV as the negative control. Group 5 (n = 6) was not vaccinated. The vaccine was administered via the intramuscular (I.M.) route at D0 and D21. Blood was collected at D21 and D39. Group 1–4 were challenged with 10⁴ PFU of USA-WA1/2020 strain at D42. Group 5 was mock-challenged with PBS. b Spike-specific serum IgG. Antibodies in post-prime (D21) and post-boost (D39) sera were measured by ELISAs. GMT endpoint titer was graphed. The error bars represent geometric SD. Statistical difference was analyzed by two-way ANOVA corrected for Dunnett’s multiple comparisons test (*p = 0.0262; ***p = 0.0006). c Neutralizing activity of serum antibodies. Post-boost sera from groups 1–4 were pooled within each group and tested in neutralization assays against USA-WA/2020 strain (WT), B.1.351 variant, and B 1.1.7 variant in technical duplicate (green: no adjuvant; yellow: adjuvanted with CpG 1018; blue: adjuvanted with AddaVax; gray: WT NDV control). Serum dilutions inhibiting 50% of the infection (ID₅₀) were plotted. (LoD = 1:50; an ID₅₀ = 1:25 was assigned to negative samples) d Body weight change of hamsters. Body weights were recorded for 5 days after challenge (green: no adjuvant; yellow: adjuvanted with CpG 1018; blue: adjuvanted with AddaVax; gray: WT NDV control; black: healthy controls). The error bars represent geometric SD. e Viral load in the lungs and nasal washes. The lower right and upper right lung lobes of a subset of animals (n = 4 for groups 1–4; n = 3 for group 5) from each group were collected at day 2 (red) and day 5 (blue) post challenge. Each lung lobe was homogenized in 1 mL PBS. Nasal washes were collected in 0.4 mL of PBS. Viral titers were measured by plaque assay on Vero E6 cells and plotted as GMT of PFU/mL (LoD = 50 PFU/mL; a titer of 25 PFU/mL was assigned to negative samples). The error bars represent geometric SD. Statistical difference was analyzed by two-way ANOVA corrected for Dunnett’s multiple comparisons test (**p = 0.0026 (WT NDV vs. no adjuvant), p = 0.0025 (WT NDV vs. CpG 1018), p = 0.0024 (WT NDV vs. AddaVax); ***p = 0.0001; ****p < 0.0001).