Fig. 1: Inactivated vaccine protects mice against SARS-CoV-2 but causes adjuvant-dependent type 2 inflammation.

a Post-boost serum-neutralizing antibody titers against SARS-CoV-2 (D614G) in mice vaccinated with inactivated influenza virus adjuvanted with aluminum hydroxide (iFLU + Alum, n = 49), inactivated SARS-CoV-2 adjuvanted with aluminum hydroxide (iCoV2 + Alum, n = 45), or inactivated SARS-CoV-2 adjuvanted with Sigma Adjuvant System adjuvant (iCoV2 + RIBI, n = 50); IC₈₀ = 80% inhibitory concentration. b, c Body weight change (b) and clinical scores (c) in iFLU + Alum (n = 12), iCoV2 + Alum (n = 19), or iCoV2 + RIBI (n = 4) vaccinated mice following challenge with SARS-CoV-2-MA10. d Pulmonary viral titers at 5 DPI following SARS-CoV-2-MA10 infection in iFLU + Alum (n = 5), iCoV2 + Alum (n = 8), or iCoV2 + RIBI (n = 4) vaccinated mice; pfu plaque-forming units. e, f Acute lung injury (ALI) (e) and diffuse alveolar damage (DAD) (f) scores in hematoxylin and eosin (H&E)-stained lungs at 5 DPI following SARS-CoV-2-MA10 infection in iFLU + Alum (n = 5), iCoV2 + Alum (n = 12), or iCoV2 + RIBI (n = 4) vaccinated mice. g, h Representative photomicrographs (g) (scale bar = 0.5 mm) and quantification (h) of pulmonary eosinophils immunohistochemically labeled for eosinophil peroxidase (EPX, brown cells) at 5 DPI following SARS-CoV-2-MA10 infection in iFLU + Alum (n = 3), iCoV2 + Alum (n = 8), or iCoV2 + RIBI (n = 4) vaccinated mice. a, d–f, h Individual data points represent independent biological replicates; solid horizontal lines and error bars represent group means ± standard deviation (SD); data analyzed by Kruskal–Wallis test with Dunn’s multiple comparisons; solid horizontal lines above data represent pairwise comparisons with p values; a, d Dotted line represents assay limit of detection. b Results reported as mean ± SD; ****p < 0.0001, iFLU + Alum versus iCoV2 + Alum, ^###p < 0.001, ^####p < 0.0001, iFLU + Alum versus iCoV2 + RIBI, two-way ANOVA with Tukey’s multiple comparisons. c Clinical scoring system: 0 = normal (blue), 1 = piloerection (orange), 2 = piloerection + kyphosis (red), 3 = piloerection, kyphosis, and reduced movement (purple), 4 = markedly reduced movement and/or labored breathing (gray), and 5 = moribund, dead or euthanized (black). Data presented as combined results from one (b, c), two (e, f, h), three (d), or four (a) independent animal experiments.