Fig. 4. SARS-CoV-2 Omicron variant spike shows impaired cell–cell fusion activity and smaller infection foci generated by live virus.
a, Schematic of the cell–cell fusion assay. The schematic was created using BioRender.com. b, Spike expression at the cell surface as determined by flow cytometry, showing the distribution of fluorescence intensity. The percentage of spike-positive cells is indicated. c, Reconstructed images of GFP+ syncytia at 16 h. d, Quantification of cell–cell fusion kinetics showing the percentage of the GFP+ area to the total cell area over time. WT, Wuhan-Hu-1 D614G. Data are mean ± s.e.m. from eight fields of views at each time point. Data are representative of at least two independent experiments. e, Three representative images of wells from 96-well plates with infection foci formed by Delta (top row) or Omicron (bottom row) live virus. Scale bars, 2 mm. f, Focus area as determined by ELISpot image analysis for Omicron (n = 111 wells) and Delta (n = 112 wells). Data are the geometric mean ± 95% CI. g, Focus number per well for the same experiments as in f. Data are the geometric mean ± 95% CI for focus number per well for Omicron and Delta infections. For f and g, statistical analysis was performed using two-sided Wilcoxon rank-sum tests; ****P < 0.0001.