inclusion criteria: * age: population aged 18 years and above; * judged by the investigator that the health condition is well after inquiry and physical examination; * vaccinated with 2 or 3 doses of inactivated covid-19 vaccine (vero cell vaccine) 6 months prior to study screening and according to product insert; * female participants who are not pregnant or nursing or at the time of enrolment (confirmed via negative urine pregnancy test), and do not have plans to become pregnant within the first 6 months after enrollment. effective contraceptive measures have been taken within 2 weeks before study inclusion and initiation; * be able and willing to provide written informed consent to participate in the study and complete all study requirements according to the study protocol;

inclusion criteria: * age: population aged 18 years and above; * judged by the investigator that the health condition is well after inquiry and physical examination; * vaccinated with 2 or 3 doses of inactivated covid-19 vaccine (vero cell vaccine) 6 months prior to study screening and according to product insert; * female participants who are not pregnant or nursing or at the time of enrolment (confirmed via negative urine pregnancy test), and do not have plans to become pregnant within the first 6 months after enrollment. effective contraceptive measures have been taken within 2 weeks before study inclusion and initiation; * be able and willing to provide written informed consent to participate in the study and complete all study requirements according to the study protocol;

inclusion criteria: age: population aged 18 years and above; judged by the investigator that the health condition is well after inquiry and physical examination; vaccinated with 2 or 3 doses of inactivated covid-19 vaccine (vero cell vaccine) 6 months prior to study screening and according to product insert; female participants who are not pregnant or nursing or at the time of enrolment (confirmed via negative urine pregnancy test), and do not have plans to become pregnant within the first 6 months after enrollment. effective contraceptive measures have been taken within 2 weeks before study inclusion and initiation; be able and willing to provide written informed consent to participate in the study and complete all study requirements according to the study protocol;

inclusion criteria: age: population aged 18 years and above; judged by the investigator that the health condition is well after inquiry and physical examination; vaccinated with 2 or 3 doses of inactivated covid-19 vaccine (vero cell vaccine) 6 months prior to study screening and according to product insert; female participants who are not pregnant or nursing or at the time of enrolment (confirmed via negative urine pregnancy test), and do not have plans to become pregnant within the first 6 months after enrollment. effective contraceptive measures have been taken within 2 weeks before study inclusion and initiation; be able and willing to provide written informed consent to participate in the study and complete all study requirements according to the study protocol;

inclusion criteria: age: population aged 18 years and above; judged by the investigator that the health condition is well after inquiry and physical examination; vaccinated with 2 doses/3 doses of inactivated covid-19 vaccine according to product insert; female subjects who are not nursing or pregnant at the time of enrolment (negative urine pregnancy test) and have no family planning within the first 6 months after enrollment. effective contraceptive measures have been taken within 2 weeks before inclusion; during the whole follow-up period of the study, be able and willing to complete the whole prescribed study plan; with self-ability to understand the study procedures, the informed consent and voluntarily sign an informed consent form and be able to comply with the requirements of the clinical study protocol.

inclusion criteria: age: population aged 18 years and above; judged by the investigator that the health condition is well after inquiry and physical examination; vaccinated with 2 doses/3 doses of inactivated covid-19 vaccine according to product insert; female subjects who are not nursing or pregnant at the time of enrolment (negative urine pregnancy test) and have no family planning within the first 6 months after enrollment. effective contraceptive measures have been taken within 2 weeks before inclusion; during the whole follow-up period of the study, be able and willing to complete the whole prescribed study plan; with self-ability to understand the study procedures, the informed consent and voluntarily sign an informed consent form and be able to comply with the requirements of the clinical study protocol.