inclusion criteria: * healthy adults aged 18-59; * have been received two doses of inactivated sars-cov-2 vaccine(coronavac)manufactured by sinovac research \& development co., ltd at an interval of 21 to 31 days for group a.have been vaccination two doses of inactivated sars-cov-2 vaccine(coronavac)manufactured by sinovac research \& development co., ltd for group b; * the subjects can understand and voluntarily sign the informed consent form; * proven legal identity.

inclusion criteria: * healthy adults aged 18-59; * have been received two doses of inactivated sars-cov-2 vaccine(coronavac)manufactured by sinovac research \& development co., ltd at an interval of 21 to 31 days for group a.have been vaccination two doses of inactivated sars-cov-2 vaccine(coronavac)manufactured by sinovac research \& development co., ltd for group b; * the subjects can understand and voluntarily sign the informed consent form; * proven legal identity.

inclusion criteria: healthy adults aged 18-59; have been received two doses of inactivated sars-cov-2 vaccine(coronavac)manufactured by sinovac research & development co., ltd at an interval of 21 to 31 days for group a.have been vaccination two doses of inactivated sars-cov-2 vaccine(coronavac)manufactured by sinovac research & development co., ltd for group b; the subjects can understand and voluntarily sign the informed consent form; proven legal identity.

inclusion criteria: healthy adults aged 18-59; have been received two doses of inactivated sars-cov-2 vaccine(coronavac)manufactured by sinovac research & development co., ltd at an interval of 21 to 31 days for group a.have been vaccination two doses of inactivated sars-cov-2 vaccine(coronavac)manufactured by sinovac research & development co., ltd for group b; the subjects can understand and voluntarily sign the informed consent form; proven legal identity.