Virus

The SARS-CoV-2 strain (registration number 43326) used in this study was isolated from a Korean patient traveling to China (the National Culture Collection for Pathogens) (Cheongju, Korea). Following plaque purification of SARS-CoV-2, this virus was cultivated twice in VERO cells with Dulbecco’s minimum essential medium (Welgene Inc., Daegu, Korea) containing 2% fetal bovine serum and 1% penicillin (10,000 IU/ml)/streptomycin (10,000 IU/ml) (Gibco, NY, United States) at 37°C in a 5% CO₂ incubator. At 3 days postinoculation (dpi), the cell supernatant was collected, centrifuged at 3,000 g for 10 min, and stored at −80°C. Virus titration was performed using VERO cells, and the 50% tissue culture infectious dose 50/ml (TCID₅₀/ml) was calculated according to the Reed–Muench method (Reed and Muench, 1938).