inclusion criteria: - adults aged 18-59; - 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 sars-cov-2 vaccine(coronavac) manufactured by sinovac research & development co., ltd at an interval of 21 to 35 days and is currently 6-8 months (180 to 240 days) after the second dose.

inclusion criteria: - adults aged 18-59; - 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 sars-cov-2 vaccine(coronavac) manufactured by sinovac research & development co., ltd at an interval of 21 to 35 days and is currently 6-8 months (180 to 240 days) after the second dose.