This is a randomized, placebo-controlled, double-blind, group comparison, multicenter study to evaluate the efficacy and safety of inhalation administration of sargramostim for 5 days, in principle (up to 10 days) as Add-on treatment to the standard treatment in COVID-19 patients.

Inclusion Criteria:

Japanese male or female subjects who have been confirmed to meet all the following criteria.

1. Hospitalized patients under treatment who were severe acute respiratory syndrome coronavirus 2 [SARS-CoV-2] positive by polymerase chain reaction (PCR) test.
2. Patients with clinically diagnosed pneumonia and a percutaneous oxygen saturation [SpO2] of 93% or less on breathing of room air at bed rest.
3. Patients for whom written informed consent has been obtained from those themselves or the legally acceptable representatives.
4. Patients aged 20 years or older and younger than 85 years at the time of obtaining informed consent.

Exclusion Criteria:

Subjects who meet any of the following criteria will be excluded. Unless otherwise stated, the following criteria refer to those at the time of screening.

1. Patients who have been participating in other intervention studies, such as studies on unapproved pharmacotherapy, within 90 days prior to screening.
2. Patients who have experienced off-label use of approved drugs (including those for COVID-19 treatment other than steroids as standard treatment) within 7 days prior to screening.
3. Patients who are not expected to survive longer than 24 hours after commencement of study drug administration.
4. Patients who are using invasive ventilator or extracorporeal membrane oxygenation (ECMO).
5. Patients who have a chronic respiratory disease requiring continuous home oxygen therapy or ventilator use.
6. Patients with an underlying condition that is considered very unlikely to withdraw ventilator (e.g., motor neuron disease, Duchenne muscular dystrophy, rapidly progressive interstitial pulmonary fibrosis).
7. Patients who have a disease including bronchial asthma, lower respiratory tract infections, and interstitial lung diseases that may affect the assessment of the clinical study, since before the symptom onset of COVID-19.
8. Patients who have a disease including leukemia and leukocytosis that causes leukocytosis.
9. Patients who have a chronic kidney disease requiring dialysis.
10. Patients who have severe liver failure (Child Pugh grade C).
11. Patients aged 80 years or older with any of heart failure, cerebrovascular disease, obesity (BMI 30 or higher), dyslipidemia, hypertension or diabetes.

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