Fig. 4: GMP lots of inactivated NDV-HXP-S produced by influenza virus vaccine manufacturers induce a protective antibody response in hamsters.

a Design of the study. Nine-to-eleven-week-old female Golden Syrian hamsters were used. Groups 1–6 (n = 8) were vaccinated with 1 µg of spike antigen of inactivated NDV-HXP-S from GPO, IVAC, and Butantan in the absence or presence of CpG 1018. Group 7 (n = 8) was vaccinated with PBS as the negative control. Group 8 (n = 8) was not vaccinated (HC, healthy controls). The vaccine was administered via the intramuscular (I.M.) route at D0 and D21. Blood was collected at D0, D21, and D33. Groups 1–7 were challenged with 10⁴ PFU of the USA-WA1/2020 strain at D35. Group 8 was mock-challenged with PBS. b Spike-specific serum IgG. Antibodies in pre-vaccination (D0, black), post-prime (D21, red), and post-boost (D33, blue) sera were measured by ELISAs (solid bars: unadjuvanted; pattern bars: adjuvanted). GMT endpoint titers were graphed. The error bars represent geometric SD. c Neutralizing activity of serum antibodies. A pseudo-particle neutralization assay was performed by Nexelis to measure neutralization titers of post-boost sera (D33). Human convalescent sera were included in the same assay as the controls (LoD = 1:25; An ID₅₀ = 1:12.5 was assigned to negative samples). d Body weight changes of hamsters. Body weights were monitored for 5 days after the challenge. The error bars represent geometric SD. e Viral load in the lungs. The lower right and upper right Lung lobes of a subset of animals (n = 4) from each group were collected at day 2 and day 5 post challenge. Each lung lobe was homogenized in 1 mL PBS. f Viral load in nasal washes and g nasal turbinates. On day 2 and day 5 post challenge, nasal washes were collected in 0.4 mL of PBS. Nasal turbinates were homogenized in 0.5 mL 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 ordinary one-way ANOVA corrected for Dunnett’s multiple comparisons test (****p < 0.0001). c–g Green: GPO; red: IVAC; blue: Butantan; gray: PBS: black: healthy controls.