Fig. 6: Efficacy of 3-2A2-4 prophylaxis against infection of the authentic SARS-CoV-2 Omicron and Delta in K18-hACE-2 mice.

a Experimental schedule for nanobody prophylaxis. Eight-week-old K18-hACE2 transgenic female mice were intraperitoneally administered with 10 mg/kg body weight of 3-2A2-4 in the format of Fc or untreated 1 day prior to challenge with 1.7 × 10³ plaque-forming units (PFU) infectious SARS-CoV-2 Omicron or 10³ PFU Delta via the intranasal route. The survival percentage b and e and body weight c and f were recorded daily after infection until the occurrence of death or until the end of experiment. The viral load in the lung tissue d and g was tested by plaque assays in the tissue homogenates at 3 days post inoculation. The limit of detection of plaque assay is 10 PFU/tissue. Data are presented as the means ± SEM. The differences between 3-2A2-4 group and untreated group are statistically significant with two-tailed p value = 0.0022 (**P < 0.01, Mann–Whitney test) in both Omicron BA.1 and Delta challenge. h, i HE and IHC staining of lung tissue from 3-2A2-4-treated or untreated mice at 3 days post inoculation. VL vascular lumen, BL bronchiolar lumen. Scale bars, 50 μm. Results presented are representatives of each group (n = 6). Source data b–g are provided as a Source Data file.