This is Double-Blind, Placebo-Controlled Multicentre Clinical Phase III Study conducted in 10 medical facilities. The objective of the study is to evaluate efficacy and safety of the drug Drug RADAMIN®VIRO, Lyophilisate for Preparation of Solution for Intramuscular and Subcutaneous Administration for COVID-19 Postexposure Prophylaxis

Upon signing the informed consent form and screening, 800 eligible subjects resides with a person with confirmed COVID-19 were randomized at a 1:1 ratio to receive either RADAMIN®VIRO once intramuscularly 5 mg (1 vial) or 1 vial of placebo once intramuscularly

Inclusion Criteria:

1. Male and female subjects aged 18 to 80 inclusive (subjects) as of the time of signing the Subject Information Sheet (SIS) Informed Consent Form.

2. A subject resides with a person with confirmed COVID-19 who meets both of the following criteria:

   • The first positive result for SARS-CoV-2 RNA laboratory test with nucleic acid amplification techniques (NAAT) or SARS-CoV-2 antigen with immunochromatographic assay, obtained up to 72 hours prior to randomisation of a subject participating in the study.
   • At least one of the symptoms typical of COVID-19 is observed, with symptoms onset no more than 5 days prior to the randomisation of the subject participating in the study.

3. Negative result for antigen of SARS-CoV-2 with immunochromatographic assay.

4. No symptoms typical of COVID-19 observed.

5. A subject is expected to continue to reside with a person with confirmed COVID-19 during the entire clinical study period; hospitalisation of a person with officially confirmed COVID-19 is not needed at the time of study subject's randomisation.

6. Subject's consent to use reliable contraception methods during the entire study and for 3 weeks after the end of the study. Reliable contraception methods are: sexual abstinence, the use of a condom combined with a spermicidal agent. Female subjects incapable of bearing children (history: hysterectomy, tubal ligation, infertility, menopause for more than 2 years), as well as male subjects with infertility or a history of vasectomy may participate in the study.

7. Availability of SIS Informed Consent Form signed and dated by a patient.

8. Availability of Informed Consent Form for collection of information on COVID-19 signed and dated by a person with confirmed COVID-19.

Exclusion Criteria:

1. Hypersensitivity to the study drug components, procaine.
2. Contraindications to intramuscular injections.
3. Contact with 2 or more persons with confirmed COVID-19 within a month prior to screening or residing with 2 or more people with officially confirmed COVID-19 at the time of screening.
4. Joint residence with more than 10 people.
5. Laboratory-confirmed case of COVID-19 within 6 months prior to randomisation.
6. Vaccination against COVID-19 within less than 4 weeks prior to screening.
7. Use or necessity to use unauthorised pharmaceuticals at the time of screening.
8. Use of immunostimulatory, immunomodulatory, or immunosuppressive medications within 3 months prior to screening.
9. Subjects undergoing renal replacement therapy or with a history of severe renal insufficiency (estimated glomerular filtration rate (GFR) < 30 ml/min/1.73 m2, calculated using the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) formula, within 6 months prior to screening).
10. Primary biliary cirrhosis class C according to the Child - Pugh classification or a history of chronic or active hepatitis B or C.
11. Positive test result for HIV, syphilis, hepatitis B and/or C at the time of screening.
12. Chronic cardiac failure, Functional Class 3 III-IV according to the New York Heart Association (NYHA) Functional Classification.
13. A history of malignant tumours, except for subjects with disease being not observed within the last 5 years, subjects with completely cured basal cell skin cancer, or completely cured carcinoma in situ.
14. Alcohol, pharmacological and/or drug dependence (history and/or at the time of screening).
15. Schizophrenia, schizoaffective disorder, bipolar disorder, or other psychiatric disorder (history or suspected) at the time of screening.
16. Any history data that may complicate, in the opinion of the investigator, interpretation of the study results or create additional risk for the subject due to his/her participation in the study.
17. Unwillingness or inability of a subject to comply with the Protocol procedures (in the opinion of the investigator).
18. Pregnant or lactating women, or women planning a pregnancy.
19. Participation in another clinical study within 3 months prior to enrolment in the present study.
20. Other conditions that prevent the subject from inclusion in the study.