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;  Exclusion Criteria:  Subjects were previously confirmed cases of COVID-19 or asymptomatic infected persons; Being allergic to any component of vaccines (including excipients) ; Injection of non-specific immunoglobulin within 1 month before enrollment; Injection of live attenuated vaccines within 1 month and injection of other vaccines within 14 days before enrollment; Subjects who have experienced severe allergic reactions to vaccines (e.g. acute anaphylaxis, urticaria, angioneurotic edema, dyspnea, etc.); Having uncontrolled epilepsy and other progressive neurological disorders and a history of Guillain-Barre syndrome; Having severe liver and kidney diseases, malignant tumors, acute diseases or acute episodes of chronic diseases; Have been diagnosed with congenital or acquired immunodeficiency, HIV infection, lymphoma, leukaemia or other autoimmune diseases; Have been diagnosed with thrombocytopenia or other clotting disorders that may contraindicate subcutaneous injection; During an acute episode of chronic bronchitis/chronic obstructive pulmonary disease; Subjects who had vaccine-related adverse reactions after the second dose; Having high fever (axillary temperature ≥39.0℃) for three days after the second dose of inoculation, or severe allergic reaction; Having any adverse nervous system reaction after the second dose; During the acute onset of a chronic disease, or the recovery of acute complications less than two weeks; Other reasons for exclusion considered by the investigator.