A 37-year-old Japanese patientundergoinghemodialysis presented with fever, chills, sore throat, and headache. There was no complaint of arthralgia, myalgia,dysgeusia, or anosmia. The first dose of the COVID-19 vaccine(Pfizer-BioNTech) was administered to the patientthree days before the presentation;exposure to a family member infected with COVID-19 had occurred two days before the presentation.The patient’s comorbidities included end-stage kidney disease, obesity (body mass index,31.2 kg/m2), diabetes mellitus, and hypertension.Upon examination, his respiratory rate was 24 breaths/min, heart rate 79 beats/min, blood pressure 149/95 mmHg, oxygen saturation 98%, and body temperature 37.9 ℃;other findings included tachypnea. Laboratory findings included elevated white blood cell count (9,470/μl [normal: 3,300-8,600 /μl]), normal platelet count (16.3 × 109/L [normal: 15.8-34.8 × 109/l]), and D-dimer of <0.5μg/ml (normal range:<1.0 μg/ml). The results of the SARS-CoV-2 antigen test of salivary specimens (FUJIREBIO, Inc., Tokyo, Japan) was 48.6pg/ml (normal range: <0.67 pg/ml). The patient had a positive result for the reverse transcriptase-polymerase chain reaction test for SARS-CoV-2, andplain computed tomography of the chest showed a focal ground-glass opacity in the right lower lobe (Figure). The patient had multiple comorbidities and was at risk of progression to severe COVID-19, thus,we recommended usingREGEN-COV. He consented to the recommended treatment. After admission, a single dose of REGEN-COV (casirivimab 1200 mg and imdevimab 1200 mg)was administered without any hypersensitivity reaction. On the second day, his respiratory rate normalized to 16 breaths/min, oxygen saturationto 98%, andbody temperature to 36.5 °C.Other clinical symptoms, including chills, sore throat, and headaches, were also resolved. His symptoms rapidlyresolved, and he was discharged after 10 days.Afterdischarge, the patient did not experience any fatigue orweakness.