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 coronavirusduring hospitalization (COVID-19).

3. After treatment, the patients have met the discharge criteria of "COVID-19Diagnosis and Treatment Guideline", and the time from hospital discharge is at least 1month at the time of enrollment. The clinical symptoms of the subjects did not worsensignificantly as compared with that at the time of discharge, and the COVID-19 nucleicacid test results are negative for at least 2 consecutive times (one of which could bethe 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 priorto initiation of any study procedures. Understands and agrees to comply with plannedstudy procedures.

5. Agrees not to participate in other drug/device studies until the study iscompleted.

Exclusion Criteria:

• 1. With one of the following respiratory diseases:

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

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

3. Subjects with following respiratory diseases such as active tuberculosis, lungcancer, sarcoidosis, pulmonary hypertension, pneumothorax, uncontrolled pleuraleffusion through intervention, pulmonary embolism, etc.;

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

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

3. Subjects, judged by investigators, with previous or current diseases, whichmay affect the participation in this study or the outcome of this study: such ascancer, diseases of heart, liver, kidney, hematopoietic system and other vitalorgans or systems, etc.

4. Patients who have undergone surgery within 1 month prior to screening and havenot fully recovered.

5. Occurrence of congestive heart failure, uncontrolled or unstable angina ormyocardial infarction, cerebrovascular accident, or history of pulmonary embolismwithin 6 months prior to screening.

6. Patients with active tuberculosis infection within 12 months prior toscreening.

7. Pregnancy or lactating women, or women of childbearing potential not agree toeither abstinence or use at least one primary form of contraception from the timeof screening till the study is completed.

8. Subjects with mental disorders or other conditions that are unable tocooperate effectively with the conduct of the clinical trial.

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