* haven't received two doses of inactivated covid-19 vaccine(coronavac); * have received covid-19 vaccines from other manufacturers; * the interval between blood collection and the second dose is less than 28 days or more than 42 days; * the subjets and their legal guardians can't cooperate to complete 3ml venous blood collection. * according to the investigator's judgment, the subject has any other factors that are not suitable for participating in the clinical trial.

* haven't received two doses of inactivated covid-19 vaccine(coronavac); * have received covid-19 vaccines from other manufacturers; * the interval between blood collection and the second dose is less than 28 days or more than 42 days; * the subjets and their legal guardians can't cooperate to complete 3ml venous blood collection. * according to the investigator's judgment, the subject has any other factors that are not suitable for participating in the clinical trial.

haven't received two doses of inactivated covid-19 vaccine(coronavac); have received covid-19 vaccines from other manufacturers; the interval between blood collection and the second dose is less than 28 days or more than 42 days; the subjets and their legal guardians can't cooperate to complete 3ml venous blood collection. according to the investigator's judgment, the subject has any other factors that are not suitable for participating in the clinical trial.

haven't received two doses of inactivated covid-19 vaccine(coronavac); have received covid-19 vaccines from other manufacturers; the interval between blood collection and the second dose is less than 28 days or more than 42 days; the subjets and their legal guardians can't cooperate to complete 3ml venous blood collection. according to the investigator's judgment, the subject has any other factors that are not suitable for participating in the clinical trial.