This is a Phase 2 prospective, randomized, placebo-controlled, double-blinded, parallel group, single administration, multi-center study to assess the safety and efficacy of efineptakin alfa single treatment compared to placebo in elderly participants (adults ≥50years) with asymptomatic or mild COVID-19

The study consists of 2 parts:

Part I - to identify the Recommended Phase 2 Dose (RP2D) compared to placebo in elderly participants (adults ≥50 years) with asymptomatic or mild COVID-19. These patients will be treated with 120 and 240 µg/kg efineptakin alfa, given on Day 1 (Baseline), respectively. The study will evaluate the safety, tolerability, and pharmacodynamics variable (ALC) of efineptakin alfa against COVID-19.

Part II - to assess the safety and efficacy of efineptakin alfa single treatment compared to placebo in elderly participants with asymptomatic or mild COVID-19.

Inclusion Criteria:

1. Adults aged 50 years and above at the time of consent
2. Subjects who have been confirmed to be COVID-19 corresponding to asymptomatic case or mild cases of severity categorization classified by FDA through authorized molecular saliva-based test or polymerase chain reaction (PCR) test and who can be available to be administered within 7 days from the onset of any symptoms.
3. Patients who provide a voluntarily consent to participate in the study and sign the consent form in his/her own handwriting.
4. Female patients of childbearing potential (including female received a tubal ligation) should be prove negative pregnancy through pregnancy test before 24 hours of the IP administration, and must be willing to maintain abstinence (restraint sexual relationships) or use an adequate method of contraception at least 90 days after the IP administration.
5. Male patients must be willing to maintain abstinence (restraint sexual relationships) or use of adequate contraception method, and not to donate sperm. Men with childbearing or pregnant female spouses should maintain abstinence or use condoms at least 90 days after the IP administration to avoid exposure to embryos
6. Patients who agree for the hospitalisation (however, the hospitalisation will be performed only if needed)

Exclusion Criteria:

1. Patients who are unable to follow clinical and follow-up procedures
2. Patients with symptoms of moderate or higher in the severity classification presented by FDA have evidence of lower respiratory tract infection in their imaging findings or need supplemental oxygen therapy or mechanical respiration (ie, non-invasive ventilation, invasive mechanical ventilation, extracorporeal membrane oxygenation, etc)
3. Patients who have clinically significant cardiovascular diseases such as myocardial infarction, unstable arrhythmia and/or unstable angina within 3 months
4. Patients who have uncontrolled type II diabetes mellitus (despite the proper use of the drug, if fasting blood sugar level is not controlled to be more than 200 mg/dL)
5. If the principal investigator determines that patients are ineligible or difficult to follow the protocol due to evidence of severe or unregulated systemic diseases, uncontrolled hypertension (despite the proper use of the drug, if the blood pressure is not controlled to be lower than 150/90 mmHg), and active bleeding tendency
6. Patients who are known to be HIV positive
7. Patients who are known to be B-type, or C-type hepatitis-positive carrier
8. Patients who are pregnant or breastfeeding
9. Patients suspected of or identified with a malignant tumor or have a history of tumors within the past 5 years
10. Patients with the infectious diseases such as bacteremia or severe pneumonia requiring active treatment within four weeks prior to the IP administration
11. Patients with immunodeficiency or autoimmune diseases that can be exacerbated through immunotherapy at present
12. Patients who have previously received an allogeneic marrow transplantation or solid organ transplantation
13. Patients who are currently taking other drugs such as immunosuppressants that may affect the results of the study
14. Patients who have severe allergy for humanized antibodies or fusion proteins, anaphylaxis, or other hypersensitivity
15. Patients who have received other IP administration while participating in another clinical trial within 30 days prior to the IP administration for this study (However, biological preparation shall be applied to 60 days and even longer period can be applied considering the half-life) -

Double blinded