1. have other significant diseases other than covid-19, that is, a disease that, according to the investigator's judgment, can cause the subject to be at risk due to participation in the study, or affect the study results and the ability of the subject to participate in the study. 2. women who are pregnant or breastfeeding or plan to be pregnant during the study. 3. subjects with one of the following respiratory diseases: 1. asthma: based on the investigator's judgment, the subjects are currently diagnosed with asthma. 2. subjects with a long-term history of copd and medication or imaging evidence of significant lung structural damage (e.g., giant pulmonary bullae). other respiratory diseases: subjects with other active pulmonry diseases, such as active tuberculosis, lung cancer, wet bronchiectasis (the high-resolution ct shows bronchiectasis, with yellow sputum every day), sarcoidosis, idiopathic interstitial pulmonary fibrosis (ipf), primary pulmonary arterial hypertension, and uncontrolled sleep apnea (the severity of the disease will affect the implementation of c)the study according to the investigator's judgment), complicated with pneumothorax, pleural effusion, pulmonary embolism, bronchial asthma, tumor, and fever of unknown origin, etc. d)lung volume reduction: subjects received lung volume reduction, lobectomy, or bronchoscopic lung volume reduction (endobronchial occlusion, airway bypass, endobronchial valve, steam thermal ablation, biological sealant and airway implant) within 6 months. e)subjects in critical or unstable conditions. critical (meeting any of the following symptoms): 1. respiratory failure occurs and mechanical ventilation is needed; 2. shock occurs; 3. with other organ failure, icu monitoring and treatment is needed. f)risk factors for pneumonia: immunosuppressive diseases (hiv), severe neurological disease affecting upper respiratory tract control, or other risk factors that the investigator believes can cause a significant risk of pneumonia in subjects. 4. subjects with serious primary diseases of heart, liver, kidney, hematopoietic system and other important organs or systems. 5. subjects with mental disorder and cognitive impairment. 6. subjects who do not follow the study steps. 7. patients with doubts about the effectiveness of informed consent: subjects with mental illness, mental retardation, poor motivation, drug abuse (including drugs and alcohol) or other disease history restricting the effectiveness of informed consent in this study. 8. use of non-expectorants and antioxidants, including large doses of vitamin c and vitamen e. 9. subjects who are not suitable for participation in this study in the judgment of investigator.

1. have other significant diseases other than covid-19, that is, a disease that, according to the investigator's judgment, can cause the subject to be at risk due to participation in the study, or affect the study results and the ability of the subject to participate in the study. 2. women who are pregnant or breastfeeding or plan to be pregnant during the study. 3. subjects with one of the following respiratory diseases: 1. asthma: based on the investigator's judgment, the subjects are currently diagnosed with asthma. 2. subjects with a long-term history of copd and medication or imaging evidence of significant lung structural damage (e.g., giant pulmonary bullae). other respiratory diseases: subjects with other active pulmonry diseases, such as active tuberculosis, lung cancer, wet bronchiectasis (the high-resolution ct shows bronchiectasis, with yellow sputum every day), sarcoidosis, idiopathic interstitial pulmonary fibrosis (ipf), primary pulmonary arterial hypertension, and uncontrolled sleep apnea (the severity of the disease will affect the implementation of c)the study according to the investigator's judgment), complicated with pneumothorax, pleural effusion, pulmonary embolism, bronchial asthma, tumor, and fever of unknown origin, etc. d)lung volume reduction: subjects received lung volume reduction, lobectomy, or bronchoscopic lung volume reduction (endobronchial occlusion, airway bypass, endobronchial valve, steam thermal ablation, biological sealant and airway implant) within 6 months. e)subjects in critical or unstable conditions. critical (meeting any of the following symptoms): 1. respiratory failure occurs and mechanical ventilation is needed; 2. shock occurs; 3. with other organ failure, icu monitoring and treatment is needed. f)risk factors for pneumonia: immunosuppressive diseases (hiv), severe neurological disease affecting upper respiratory tract control, or other risk factors that the investigator believes can cause a significant risk of pneumonia in subjects. 4. subjects with serious primary diseases of heart, liver, kidney, hematopoietic system and other important organs or systems. 5. subjects with mental disorder and cognitive impairment. 6. subjects who do not follow the study steps. 7. patients with doubts about the effectiveness of informed consent: subjects with mental illness, mental retardation, poor motivation, drug abuse (including drugs and alcohol) or other disease history restricting the effectiveness of informed consent in this study. 8. use of non-expectorants and antioxidants, including large doses of vitamin c and vitamen e. 9. subjects who are not suitable for participation in this study in the judgment of investigator.

have other significant diseases other than covid-19, that is, a disease that, according to the investigator's judgment, can cause the subject to be at risk due to participation in the study, or affect the study results and the ability of the subject to participate in the study. women who are pregnant or breastfeeding or plan to be pregnant during the study. subjects with one of the following respiratory diseases: asthma: based on the investigator's judgment, the subjects are currently diagnosed with asthma. subjects with a long-term history of copd and medication or imaging evidence of significant lung structural damage (e.g., giant pulmonary bullae). other respiratory diseases: subjects with other active pulmonry diseases, such as active tuberculosis, lung cancer, wet bronchiectasis (the high-resolution ct shows bronchiectasis, with yellow sputum every day), sarcoidosis, idiopathic interstitial pulmonary fibrosis (ipf), primary pulmonary arterial hypertension, and uncontrolled sleep apnea (the severity of the disease will affect the implementation of c)the study according to the investigator's judgment), complicated with pneumothorax, pleural effusion, pulmonary embolism, bronchial asthma, tumor, and fever of unknown origin, etc. d)lung volume reduction: subjects received lung volume reduction, lobectomy, or bronchoscopic lung volume reduction (endobronchial occlusion, airway bypass, endobronchial valve, steam thermal ablation, biological sealant and airway implant) within 6 months. e)subjects in critical or unstable conditions. critical (meeting any of the following symptoms): 1. respiratory failure occurs and mechanical ventilation is needed; 2. shock occurs; 3. with other organ failure, icu monitoring and treatment is needed. f)risk factors for pneumonia: immunosuppressive diseases (hiv), severe neurological disease affecting upper respiratory tract control, or other risk factors that the investigator believes can cause a significant risk of pneumonia in subjects. subjects with serious primary diseases of heart, liver, kidney, hematopoietic system and other important organs or systems. subjects with mental disorder and cognitive impairment. subjects who do not follow the study steps. patients with doubts about the effectiveness of informed consent: subjects with mental illness, mental retardation, poor motivation, drug abuse (including drugs and alcohol) or other disease history restricting the effectiveness of informed consent in this study. use of non-expectorants and antioxidants, including large doses of vitamin c and vitamen e. subjects who are not suitable for participation in this study in the judgment of investigator.

have other significant diseases other than covid-19, that is, a disease that, according to the investigator's judgment, can cause the subject to be at risk due to participation in the study, or affect the study results and the ability of the subject to participate in the study. women who are pregnant or breastfeeding or plan to be pregnant during the study. subjects with one of the following respiratory diseases: asthma: based on the investigator's judgment, the subjects are currently diagnosed with asthma. subjects with a long-term history of copd and medication or imaging evidence of significant lung structural damage (e.g., giant pulmonary bullae). other respiratory diseases: subjects with other active pulmonry diseases, such as active tuberculosis, lung cancer, wet bronchiectasis (the high-resolution ct shows bronchiectasis, with yellow sputum every day), sarcoidosis, idiopathic interstitial pulmonary fibrosis (ipf), primary pulmonary arterial hypertension, and uncontrolled sleep apnea (the severity of the disease will affect the implementation of c)the study according to the investigator's judgment), complicated with pneumothorax, pleural effusion, pulmonary embolism, bronchial asthma, tumor, and fever of unknown origin, etc. d)lung volume reduction: subjects received lung volume reduction, lobectomy, or bronchoscopic lung volume reduction (endobronchial occlusion, airway bypass, endobronchial valve, steam thermal ablation, biological sealant and airway implant) within 6 months. e)subjects in critical or unstable conditions. critical (meeting any of the following symptoms): 1. respiratory failure occurs and mechanical ventilation is needed; 2. shock occurs; 3. with other organ failure, icu monitoring and treatment is needed. f)risk factors for pneumonia: immunosuppressive diseases (hiv), severe neurological disease affecting upper respiratory tract control, or other risk factors that the investigator believes can cause a significant risk of pneumonia in subjects. subjects with serious primary diseases of heart, liver, kidney, hematopoietic system and other important organs or systems. subjects with mental disorder and cognitive impairment. subjects who do not follow the study steps. patients with doubts about the effectiveness of informed consent: subjects with mental illness, mental retardation, poor motivation, drug abuse (including drugs and alcohol) or other disease history restricting the effectiveness of informed consent in this study. use of non-expectorants and antioxidants, including large doses of vitamin c and vitamen e. subjects who are not suitable for participation in this study in the judgment of investigator.

1. have other significant diseases other than covid-19, that is, a disease that, according to the investigator's judgment, can cause the subject to be at risk due to participation in the study, or affect the study results and the ability of the subject to participate in the study. 2. women who are pregnant or breastfeeding or plan to be pregnant during the study. 3. subjects with one of the following respiratory diseases: 1. asthma: based on the investigator's judgment, the subjects are currently diagnosed with asthma. 2. subjects with a long-term history of copd and medication or imaging evidence of significant lung structural damage (e.g., giant pulmonary bullae). other respiratory diseases: subjects with other active pulmonry diseases, such as active tuberculosis, lung cancer, wet bronchiectasis (the high-resolution ct shows bronchiectasis, with yellow sputum every day), sarcoidosis, idiopathic interstitial pulmonary fibrosis (ipf), primary pulmonary arterial hypertension, and uncontrolled sleep apnea (the severity of the disease will affect the implementation of c)the study according to the investigator's judgment), complicated with pneumothorax, pleural effusion, pulmonary embolism, bronchial asthma, tumor, and fever of unknown origin, etc. d)lung volume reduction: subjects received lung volume reduction, lobectomy, or bronchoscopic lung volume reduction (endobronchial occlusion, airway bypass, endobronchial valve, steam thermal ablation, biological sealant and airway implant) within 6 months. e)subjects in critical or unstable conditions. critical (meeting any of the following symptoms): 1. respiratory failure occurs and mechanical ventilation is needed; 2. shock occurs; 3. with other organ failure, icu monitoring and treatment is needed. f)risk factors for pneumonia: immunosuppressive diseases (hiv), severe neurological disease affecting upper respiratory tract control, or other risk factors that the investigator believes can cause a significant risk of pneumonia in subjects. 4. subjects with serious primary diseases of heart, liver, kidney, hematopoietic system and other important organs or systems. 5. subjects with mental disorder and cognitive impairment. 6. subjects who do not follow the study steps. 7. patients with doubts about the effectiveness of informed consent: subjects with mental illness, mental retardation, poor motivation, drug abuse (including drugs and alcohol) or other disease history restricting the effectiveness of informed consent in this study. 8. use of non-expectorants and antioxidants, including large doses of vitamin c and vitamen e. 9. subjects who are not suitable for participation in this study in the judgment of investigator.

1. have other significant diseases other than covid-19, that is, a disease that, according to the investigator's judgment, can cause the subject to be at risk due to participation in the study, or affect the study results and the ability of the subject to participate in the study. 2. women who are pregnant or breastfeeding or plan to be pregnant during the study. 3. subjects with one of the following respiratory diseases: 1. asthma: based on the investigator's judgment, the subjects are currently diagnosed with asthma. 2. subjects with a long-term history of copd and medication or imaging evidence of significant lung structural damage (e.g., giant pulmonary bullae). other respiratory diseases: subjects with other active pulmonry diseases, such as active tuberculosis, lung cancer, wet bronchiectasis (the high-resolution ct shows bronchiectasis, with yellow sputum every day), sarcoidosis, idiopathic interstitial pulmonary fibrosis (ipf), primary pulmonary arterial hypertension, and uncontrolled sleep apnea (the severity of the disease will affect the implementation of c)the study according to the investigator's judgment), complicated with pneumothorax, pleural effusion, pulmonary embolism, bronchial asthma, tumor, and fever of unknown origin, etc. d)lung volume reduction: subjects received lung volume reduction, lobectomy, or bronchoscopic lung volume reduction (endobronchial occlusion, airway bypass, endobronchial valve, steam thermal ablation, biological sealant and airway implant) within 6 months. e)subjects in critical or unstable conditions. critical (meeting any of the following symptoms): 1. respiratory failure occurs and mechanical ventilation is needed; 2. shock occurs; 3. with other organ failure, icu monitoring and treatment is needed. f)risk factors for pneumonia: immunosuppressive diseases (hiv), severe neurological disease affecting upper respiratory tract control, or other risk factors that the investigator believes can cause a significant risk of pneumonia in subjects. 4. subjects with serious primary diseases of heart, liver, kidney, hematopoietic system and other important organs or systems. 5. subjects with mental disorder and cognitive impairment. 6. subjects who do not follow the study steps. 7. patients with doubts about the effectiveness of informed consent: subjects with mental illness, mental retardation, poor motivation, drug abuse (including drugs and alcohol) or other disease history restricting the effectiveness of informed consent in this study. 8. use of non-expectorants and antioxidants, including large doses of vitamin c and vitamen e. 9. subjects who are not suitable for participation in this study in the judgment of investigator.