Study to Assess Efficacy and Safety of Treamid for Patients With Reduced Exercise Tolerance After COVID-19

14-18 Russian centers are planned for participation in this study. The study consists of three periods: screening (2 weeks), treatment period (4 weeks) and follow-up period (4 weeks after completion of treatment with Treamid / Placebo). 412 patients with persistent lung damage and reduced exercise tolerance exertion after COVID-19 pneumonia are planned to be randomized. Patients will be evaluated using the Modified British Medical Research Council (mMRC), six-minute walk test (6-MWT), Borg scale for dyspnea and fatigue, Dyspnea scale Index (BDI and TDI), KBILD questionnaire, EQ-5D-3L questionnaire, Hospital Anxiety and Depression Scale (HADS), Modified Fatigue Impact Scale (MFIS), Clinical Global Impression rating scales (CGI-I and CGI-S), chest computed tomography (CT), spirometry and body plethysmography with determination of DLCO. All eligible patients will be randomized into 4 groups of 103 patients each in a 1:1:1:1 ratio: Treamid 25 mg in the morning and Placebo in the evening daily, Treamid 25 mg in the morning and Treamid 25 mg in the evening daily, Treamid 50 mg in the morning and Placebo in the evening daily, Placebo in the morning and Placebo in the evening daily. Patients will visit the study center at the Week 1, Week 2, Week 4 of treatment period and at the end of the follow up period. During all visits will be evaluated Adverse events (AEs), concomitant therapy, investigational drug registration, body weight, vital signs and Oxygen saturation (SpO2) scores. 6-MWT, Borg scale for dyspnea and fatigue, Dyspnea scale Index (TDI), KBILD questionnaire and MFIS will be also evaluated.