The purpose of this clinical trial is to assess the safety and efficacy of Clevudine 120 mg versus placebo once daily administration with standard of care therapy for 14 days (maximum up to 21 days) in patients with moderate COVID-19.

Key Inclusion Criteria:

1. Over 19 years of age

2. COVID-19 confirmed by a real-time RT-PCR tests 4 days prior to clinical trial enrollment

3. Patients with peripheral capillary oxygen saturation (SPO2) greater than 94% at the time of screening

4. Patients whose body temperature is measured according to the measured area without taking a fever reducer during screening:

   [armpit of greater than 37.0 °C or an oral of greater than 37.2 °C; Patients with rectum greater than 37.6 °C or eardrum greater than 37.5 °C] (Notes: Although you take a fever reducer, you can still be enrolled in after investigator's judgement whether there is fever or not.)

5. Patients with evidence of lung invasions as a result of radiation tests

Exclusion Criteria:

1. Patients who need breathing device (for example, Invasive ventilation, Invasive mechanical ventilation, Extra-corporeal membrane oxygenation).
2. Patients who participated in other clinical trials related to COVID-19.
3. Patients who were administered drugs directly to COVID-19 24 hours prior to the start of the study.
4. Patients whose AST or ALT has increased by more than 5 times the normal lab value.