inclusion criteria: * subjects aged 60 and above with full capacity for civil conduct; * chronic bronchitis (or chronic obstructive pulmonary disease) diagnosed by a medical institution at level i or above; * body temperature \< 37.3 ° c confirmed by clinical examination before enrollment ; * able and willing to complete the entire study plan during the study follow-up period; * have the ability to understand the study procedures, voluntarily sign informed consent, and comply with the requirements of the clinical study protocol; * subjects participating in the past clinical trial have completed two doses of covid-19 vaccine and blood collection before and after immunization;

inclusion criteria: * subjects aged 60 and above with full capacity for civil conduct; * chronic bronchitis (or chronic obstructive pulmonary disease) diagnosed by a medical institution at level i or above; * body temperature \< 37.3 ° c confirmed by clinical examination before enrollment ; * able and willing to complete the entire study plan during the study follow-up period; * have the ability to understand the study procedures, voluntarily sign informed consent, and comply with the requirements of the clinical study protocol; * subjects participating in the past clinical trial have completed two doses of covid-19 vaccine and blood collection before and after immunization;

inclusion criteria: - subjects aged 60 and above with full capacity for civil conduct; - chronic bronchitis (or chronic obstructive pulmonary disease) diagnosed by a medical institution at level i or above; - body temperature < 37.3 ° c confirmed by clinical examination before enrollment ; - able and willing to complete the entire study plan during the study follow-up period; - have the ability to understand the study procedures, voluntarily sign informed consent, and comply with the requirements of the clinical study protocol; - subjects participating in the past clinical trial have completed two doses of covid-19 vaccine and blood collection before and after immunization;

inclusion criteria: - subjects aged 60 and above with full capacity for civil conduct; - chronic bronchitis (or chronic obstructive pulmonary disease) diagnosed by a medical institution at level i or above; - body temperature < 37.3 ° c confirmed by clinical examination before enrollment ; - able and willing to complete the entire study plan during the study follow-up period; - have the ability to understand the study procedures, voluntarily sign informed consent, and comply with the requirements of the clinical study protocol; - subjects participating in the past clinical trial have completed two doses of covid-19 vaccine and blood collection before and after immunization;