Figure 1

The B1.617.2 variant is more virulent than the Hu-1 strain in K18-hACE2 mice. The schematic illustration of the animal experiment. K18-hACE2 mice were intranasally inoculated with the Hu-1 strain or B1.617.2 variant (A). Weight loss and mortality were monitored in K18-hACE2 mice after inoculation with the indicated strains (B). Representative data were analyzed from three independent experiments and presented as the mean ± SEM value (n = 12). The viral burden (C) and negative-sense strand (D) in the lungs and brains were quantified by qRT-PCR at the indicated times after infection. The titration of SARS-CoV-2 in the lungs and brains was performed by TCID₅₀ for the infectious virus (E). Western blotting detected the N protein of SARS-CoV-2 in the lung and brain homogenates at the indicated times after infection (F). Two-way ANOVA was performed, followed by Dunnett’s multiple-comparison tests. Statistical significance is indicated by asterisks (n = 5, *p < 0.05, **p < 0.01, ***p < 001, ****p < 0.0001, ns not significant). C, Control; H, Hu-1; B, B1.617.2. The viral RNA copies and infectious SARS-CoV-2 limit of detection were log₁₀/copies and 2 log₁₀ TCID₅₀/mL, respectively (dot line). The image J software (version 1.53 k, http://imagej.nih.gov/ij/) normalized the relative viral N protein expression with β-actin.