Efficacy and Safety of Polyoxidonium® in Hospitalized Patients With Coronavirus Disease COVID-19

Inclusion Criteria: 1. Male and female patients from 18 to 85 years of age. 2. The patient (or his/her legal representative, if the patient is not able to sign the form) signed an Informed Consent form for participation in this study before any initiation of any study procedures. 3. The patient can understand all protocol requirements, perform the study procedures, and agree to all limitations specified in the protocol. 4. Confirmed diagnosis of coronavirus disease (COVID-19): laboratory-confirmed SARS-CoV-2 infection as determined by PCR, or other commercial or public health assay in any specimen \< 14 days prior to randomization. 5. Illness (coronavirus disease COVID-19) of any duration, and at least one of the following: * Radiographic/tomographic chest infiltrates by imaging (chest x-ray, CT scan, etc.), OR * Evidence of rales/crackles on clinical exam AND SpO2 ≤ 94% on room air, OR * Indications for mechanical ventilation and/or supplemental oxygen. 6. Agrees to use adequate contraception methods (the methods with at least 90% efficacy include non-hormonal intrauterine devices; condom with intravaginal spermicide; cervical caps Exclusion Criteria: 1. History of clinically significant allergic reactions. 2. Hypersensitivity and/or intolerability to any ingredient of the investigational product or placebo. 3. Anticipated transfer to another hospital which is not a study centre within the next 72 hours. 4. Acute or chronic renal failure. 5. History of HIV infection, tuberculosis. 6. Conditions associated with primary immunodeficiency. 7. Concomitant use of cytostatic medications to treat a concomitant disease. 8. Systemic connective tissue diseases. 9. Need for the prohibited medications. 10. Administration of medications that are prohibited or unauthorized by the protocol within 2 weeks before the expected randomization date. 11. History of alcohol or drug dependence. 12. History of malignant tumours of any location with remission for less than 2 years. 13. History of psychic (including depressive) disorders, physical and other factors that do not allow for adequate self-assessment of one's behaviour and for compliance with the protocol requirements, including history of psychiatric disorders. 14. Pregnancy or breastfeeding. 15. Intravenous injections and/or sampling of the required amount of blood is not possible. 16. Positive pregnancy test (in patients with childbearing potential). 17. Participation in any clinical study within 3 months before enrolment in this study. 18. History of any condition that the study doctor considers significant enough to prevent enrolment of this patient.