inclusion criteria: - age ≥ 18 years old, - through asking medical history and physical examination, the investigator judged that the health condition is good: the chronic disease is stable and there is no change within 3 months of medication; - has been completed 2 doses of covid-19 inactivated vaccine 4-8 months ago; - female participants of childbearing age who were not breast-feeding or pregnant (negative blood pregnancy test), and had no family planning in the first 3 months after enrollment and took effective contraceptive measures. take effective contraceptive measures within 2 weeks before inclusion; - volunteered to receive the third dose of vaccine.and during the entire follow-up research period, be able and willing to complete the entire prescribed research plan; have the ability to self-understand research procedures, informed consent & voluntarily sign informed consent, and be able to comply with the requirements of the plan

inclusion criteria: - age ≥ 18 years old, - through asking medical history and physical examination, the investigator judged that the health condition is good: the chronic disease is stable and there is no change within 3 months of medication; - has been completed 2 doses of covid-19 inactivated vaccine 4-8 months ago; - female participants of childbearing age who were not breast-feeding or pregnant (negative blood pregnancy test), and had no family planning in the first 3 months after enrollment and took effective contraceptive measures. take effective contraceptive measures within 2 weeks before inclusion; - volunteered to receive the third dose of vaccine.and during the entire follow-up research period, be able and willing to complete the entire prescribed research plan; have the ability to self-understand research procedures, informed consent & voluntarily sign informed consent, and be able to comply with the requirements of the plan