Hydrogen-oxygen Gas Mixture Inhalation in Patients With Convalescent Coronavirus Disease 2019 (COVID-19)

Inclusion Criteria:

- 1） Male or female, aged between 18 and 75 (including boundary values) at screening.

2) Severe or critically ill patients who have been diagnosed with a novel coronavirus
during hospitalization (COVID-19).

3) After treatment, the patients have met the discharge criteria of "COVID-19
Diagnosis and Treatment Guideline", and the time from hospital discharge is at least 1
month at the time of enrollment. The clinical symptoms of the subjects did not worsen
significantly as compared with that at the time of discharge, and the COVID-19 nucleic
acid test results are negative for at least 2 consecutive times (one of which could be
the nucleic acid test before discharge).

4) Forced vital capacity/per predicted (FVC% pred) ≥ 50%. 5) 50% ≤ FEV1 %pred ≤80%。 6)
Subject (or legally authorized representative) provides written informed consent prior
to initiation of any study procedures. Understands and agrees to comply with planned
study procedures.

7) Agrees not to participate in other drug/device studies until the study is
completed.

Exclusion Criteria:

- 1) With one of the following respiratory diseases:

1. Subjects with asthma history, or cannot rule out asthma based on the diagnosis of
investigator;

2. Subjects with chronic obstructive pulmonary disease (COPD);

3. Subjects with following respiratory diseases such as active tuberculosis, lung
cancer, sarcoidosis, pulmonary hypertension, pneumothorax, uncontrolled pleural
effusion through intervention, pulmonary embolism, etc.;

4. Lung volume reduction: subjects have had lung volume reduction surgery, pulmonary
lobectomy, or bronchoscopic lung volume reduction surgery.

2) Subjects with pulmonary heart disease. 3) Patients who are scheduled for
elective surgery during the study period, such as thoracic and abdominal major
surgery.

4) Subjects, judged by investigators, with previous or current diseases, which
may affect the participation in this study or the outcome of this study: such as
cancer, diseases of heart, liver, kidney, hematopoietic system and other vital
organs or systems, etc.

5) Patients who have undergone surgery within 1 month prior to screening and have
not fully recovered.

6) Occurrence of congestive heart failure, uncontrolled or unstable angina or
myocardial infarction, cerebrovascular accident, or history of pulmonary embolism
within 6 months prior to screening.

7) Patients with active tuberculosis infection within 12 months prior to
screening.

8) Pregnancy or lactating women, or women of childbearing potential not agree to
either abstinence or use at least one primary form of contraception from the time
of screening till the study is completed.

9) Subjects with mental disorders or other conditions that are unable to
cooperate effectively with the conduct of the clinical trial.

10) Subjects intolerance to inhalation therapy. 11) Others whom the investigator
or sub-investigator judged inappropriate for participation in the study.