Inclusion Criteria:

1. Voluntary written consent to participate in the trial

2. Age≥ 19 years

3. Diagnosed as COVID-19: the definitive diagnosis of COVID-19 will be made at a
healthcare facility based on COVID-19 tests approved in Korea, such as reverse
transcription polymerase chain reaction (RT-PCR), Xpert, film array, and rapid
antigen test (RAT).

4. The diagnosis of persistent COVID-19 will be made following the criteria below:

1. No improvement or worsening of symptoms/signs of active inflammation, such as fever,
pneumonia, and dyspnea requiring oxygen, even after 2 weeks of the initial symptom
onset or diagnosis of COVID-19 (persisting symptoms/signs at or after the third week
of illness).

2. The day count for the disease course is based on the symptom onset or diagnosis
date, whichever is earlier, with Day 1 being the date of symptom onset or diagnosis.
The third week refers to the period including and following Day 15. For the purpose
of day count calculation, self-test results using RAT are accepted.

3. Both symptoms and signs indicative of active inflammation must be present. This
status corresponds to the Modified WHO clinical progression scale of ≥ 4.

- Symptoms include at least one of the following.

1. Fever of 37.8°C or higher lasting for >48 h (determined based on
self-measurement and statements from the patient or caregiver, with fevers
persisting from Day 13 to Day 15 also accepted)

2. Persistent cough despite taking appropriate expectorants and cough
suppressants

3. Dyspnea upon walking on a flat surface (modified Medical Research Council
grade >2) ② At least one of the following signs of active inflammation
must be present.

1. Pulmonary infiltration suggestive of COVID-19 observed in chest radiograph
or computed tomography scan findings. Findings may vary, from ground-glass
opacities to patchy consolidation, and are determined by the clinician or
radiologist.

2. Decreased oxygen saturation (PaO2/FiO2 ≤300 mmHg, SpO2 ≤92%, or PaO2 ≤63%)
5. Cases of patients with B-cell impairment:

(1) Patients with B-cell lineage hematologic malignancies, such as B-cell lymphoma or
multiple myeloma, who are presumed to have impaired B-cell function owing to B-cell
targeting chemotherapy (i.e., those receiving rituximab, CAR-T, Bispecific T-cell engager
therapies), or second-line or higher treatments, such as autologous stem cell
transplantation (AutoPBSCT) (2) Patients suffering from diseases known to result in
B-cell depletion, such as Good's syndrome associated with thymoma (3) Cases of patients
with a congenital primary immunodeficiency who have reduced antibody formation and have
not undergone IVIG replacement in the past 3 months.

Among these, those who received B-cell targeting chemotherapy within the past 3 months
are eligible for enrollment based on clinical criteria, but other patients must confirm
the reduction of peripheral B cells to <1% via flow cytometry to be eligible for
enrollment.

Exclusion Criteria:

1. Difficulty controlling the underlying disease or life expectancy of <3 months even
after COVID-19 is successfully treated.

2. T-cell impairment.

(1)T-cell suppressive drugs (e.g., cyclosporine, tacrolimus) cannot be suspended owing to
organ transplantation or autoimmune disorder.

(2) Patients with human immunodeficiency virus (HIV) infection with a CD4 T-cell count
<500 cells/μL or persistent detection of HIV viral RNA in the blood.

3. IVIG or COVID-19 convalescent plasma therapy within 3 months of screening 4. History
of serious reaction or hypersensitivity to blood, blood products, blood-derived
products, IVIG, and IgG 5. Immunoglobulin A (IgA) deficiency or IgA antibodies
present 6. Uncontrolled hypertension (systolic blood pressure > 160 mmHg or
diastolic blood pressure > 100 mmHg) 7. Hemolytic anemia, hemorrhagic anemia 8.
Impaired cardiac function [New York Heart Association Functional Class Ⅲ or IV] 9.
High risk for thrombosis/embolism clinically owing to a history of cerebrovascular
and cardiovascular disorders, thrombosis, or embolism 10. Cases of pregnant or
breastfeeding women 11. Current participation in another clinical trial related to
COVID-19 drugs 12. Cases of participants that are inappropriate to participate in
the trial based on the investigator's discretion