inclusion criteria: * healthy participants aged 18 years and above; * proven legal identity; * the subjects can understand and voluntarily sign the informed consent form and be willing to complete the study in accordance with the study plan; * have received two doses of inactivated covid-19 vaccine (coronavac®) manufactured by sinovac research \& development co., ltd and that is currently 5-9 months after the second dose.

inclusion criteria: * healthy participants aged 18 years and above; * proven legal identity; * the subjects can understand and voluntarily sign the informed consent form and be willing to complete the study in accordance with the study plan; * have received two doses of inactivated covid-19 vaccine (coronavac®) manufactured by sinovac research \& development co., ltd and that is currently 5-9 months after the second dose.

inclusion criteria: healthy participants aged 18 years and above; proven legal identity; the subjects can understand and voluntarily sign the informed consent form and be willing to complete the study in accordance with the study plan; have received two doses of inactivated covid-19 vaccine (coronavac®) manufactured by sinovac research & development co., ltd and that is currently 5-9 months after the second dose.

inclusion criteria: healthy participants aged 18 years and above; proven legal identity; the subjects can understand and voluntarily sign the informed consent form and be willing to complete the study in accordance with the study plan; have received two doses of inactivated covid-19 vaccine (coronavac®) manufactured by sinovac research & development co., ltd and that is currently 5-9 months after the second dose.