inclusion criteria: * adults aged 18 years and older at time of consent, male or female; * normal body temperature; * meet either of the following conditions: 1. received completed primary immunization of 2 doses of coronavac 6-15 months ago; 2. received completed 3 doses of coronavac 5-9 months ago; * female participants who are not pregnant at the time of enrollment (urine pregnancy test is negative), nor during lactating; and has no birth plan and agree to take effective contraception in 7 months after enrollment; and took effective and acceptable contraceptive methods in the previous 2 weeks before the enrollment; * be able and willing to complete the study during the entire study and follow-up period; * participants who have the ability to understand the study process, sign the informed consent form voluntarily , and be able to comply with the requirements of the clinical study protocol.

inclusion criteria: * adults aged 18 years and older at time of consent, male or female; * normal body temperature; * meet either of the following conditions: 1. received completed primary immunization of 2 doses of coronavac 6-15 months ago; 2. received completed 3 doses of coronavac 5-9 months ago; * female participants who are not pregnant at the time of enrollment (urine pregnancy test is negative), nor during lactating; and has no birth plan and agree to take effective contraception in 7 months after enrollment; and took effective and acceptable contraceptive methods in the previous 2 weeks before the enrollment; * be able and willing to complete the study during the entire study and follow-up period; * participants who have the ability to understand the study process, sign the informed consent form voluntarily , and be able to comply with the requirements of the clinical study protocol.

inclusion criteria: adults aged 18 years and older at time of consent, male or female; normal body temperature; meet either of the following conditions: received completed primary immunization of 2 doses of coronavac 6-15 months ago; received completed 3 doses of coronavac 5-9 months ago; female participants who are not pregnant at the time of enrollment (urine pregnancy test is negative), nor during lactating; and has no birth plan and agree to take effective contraception in 7 months after enrollment; and took effective and acceptable contraceptive methods in the previous 2 weeks before the enrollment; be able and willing to complete the study during the entire study and follow-up period; participants who have the ability to understand the study process, sign the informed consent form voluntarily , and be able to comply with the requirements of the clinical study protocol.

inclusion criteria: adults aged 18 years and older at time of consent, male or female; normal body temperature; meet either of the following conditions: received completed primary immunization of 2 doses of coronavac 6-15 months ago; received completed 3 doses of coronavac 5-9 months ago; female participants who are not pregnant at the time of enrollment (urine pregnancy test is negative), nor during lactating; and has no birth plan and agree to take effective contraception in 7 months after enrollment; and took effective and acceptable contraceptive methods in the previous 2 weeks before the enrollment; be able and willing to complete the study during the entire study and follow-up period; participants who have the ability to understand the study process, sign the informed consent form voluntarily , and be able to comply with the requirements of the clinical study protocol.