K18-hACE2 transgenic mice that were intraperitoneally injected with WT-VHH/12GS-WT-Fc (5 mg/kg) and challenged 7 hours later with a dose of 8 × 103 plaque-forming units (PFU) of a clinical isolate of SARS-CoV-2 displayed no body weight loss, survived viral challenge, and had significantly reduced lung virus titers on day 3 after infection compared to control-treated animals (P = 0.0015 and P = 0,0379, respectively; Fig. 1, A to C). Here, KRT18 is linked to infection.