inclusion criteria: potential participants must meet all inclusion criteria to be enrolled and participate in the study, as follows: 1. adult male or female aged 18 years or more on the day of signing the icf, confirmed by identification cards. 2. verified, documentation of past covid-19 vaccination i. study part a: having completed the 2-dose homologous primary regimen (21 to 35 days apart) of inactivated covid-19 vaccine of either sinovac-sinovac or sinopharm-sinopharm ii. study part b: having received one dose of inactivated covid-19 vaccine of either sinovac or sinopharm with the appropriate interval period 3. women of childbearing potential who are test negative with a highly sensitive urine pregnancy test at visit 1, prior to study vaccine administration. 4. subject has provided written informed consent prior to performance of any study-specific procedures and is willing and has means to be contacted and to contact the investigator during the study. 5. in the investigator's clinical judgment, the participant is in good health, or has stable and well-controlled medical conditions. 6. participant agrees to not donate bone marrow, blood, and blood products from the study vaccine administration until 3 months after receiving the study vaccine.

inclusion criteria: potential participants must meet all inclusion criteria to be enrolled and participate in the study, as follows: 1. adult male or female aged 18 years or more on the day of signing the icf, confirmed by identification cards. 2. verified, documentation of past covid-19 vaccination i. study part a: having completed the 2-dose homologous primary regimen (21 to 35 days apart) of inactivated covid-19 vaccine of either sinovac-sinovac or sinopharm-sinopharm ii. study part b: having received one dose of inactivated covid-19 vaccine of either sinovac or sinopharm with the appropriate interval period 3. women of childbearing potential who are test negative with a highly sensitive urine pregnancy test at visit 1, prior to study vaccine administration. 4. subject has provided written informed consent prior to performance of any study-specific procedures and is willing and has means to be contacted and to contact the investigator during the study. 5. in the investigator's clinical judgment, the participant is in good health, or has stable and well-controlled medical conditions. 6. participant agrees to not donate bone marrow, blood, and blood products from the study vaccine administration until 3 months after receiving the study vaccine.

inclusion criteria: potential participants must meet all inclusion criteria to be enrolled and participate in the study, as follows: adult male or female aged 18 years or more on the day of signing the icf, confirmed by identification cards. verified, documentation of past covid-19 vaccination i. study part a: having completed the 2-dose homologous primary regimen (21 to 35 days apart) of inactivated covid-19 vaccine of either sinovac-sinovac or sinopharm-sinopharm ii. study part b: having received one dose of inactivated covid-19 vaccine of either sinovac or sinopharm with the appropriate interval period women of childbearing potential who are test negative with a highly sensitive urine pregnancy test at visit 1, prior to study vaccine administration. subject has provided written informed consent prior to performance of any study-specific procedures and is willing and has means to be contacted and to contact the investigator during the study. in the investigator's clinical judgment, the participant is in good health, or has stable and well-controlled medical conditions. participant agrees to not donate bone marrow, blood, and blood products from the study vaccine administration until 3 months after receiving the study vaccine.

inclusion criteria: potential participants must meet all inclusion criteria to be enrolled and participate in the study, as follows: adult male or female aged 18 years or more on the day of signing the icf, confirmed by identification cards. verified, documentation of past covid-19 vaccination i. study part a: having completed the 2-dose homologous primary regimen (21 to 35 days apart) of inactivated covid-19 vaccine of either sinovac-sinovac or sinopharm-sinopharm ii. study part b: having received one dose of inactivated covid-19 vaccine of either sinovac or sinopharm with the appropriate interval period women of childbearing potential who are test negative with a highly sensitive urine pregnancy test at visit 1, prior to study vaccine administration. subject has provided written informed consent prior to performance of any study-specific procedures and is willing and has means to be contacted and to contact the investigator during the study. in the investigator's clinical judgment, the participant is in good health, or has stable and well-controlled medical conditions. participant agrees to not donate bone marrow, blood, and blood products from the study vaccine administration until 3 months after receiving the study vaccine.

inclusion criteria: potential participants must meet all inclusion criteria to be enrolled and participate in the study, as follows: adult male or female aged 18 years or more on the day of signing the icf, confirmed by identification cards. verified, documentation of past covid-19 vaccination i. study part a: having completed the 2-dose homologous primary regimen (21 to 28 days apart) of inactivated covid-19 vaccine of either sinovac-sinovac or sinopharm-sinopharm ii. study part b: having received one dose of inactivated covid-19 vaccine of either sinovac or sinopharm with the appropriate interval period subject has provided written informed consent prior to performance of any study-specific procedures and is willing and has means to be contacted and to contact the investigator during the study. in the investigator's clinical judgment, the participant is in good health, or has stable and well-controlled medical conditions. participant agrees to not donate bone marrow, blood, and blood products from the study vaccine administration until 3 months after receiving the study vaccine.

inclusion criteria: potential participants must meet all inclusion criteria to be enrolled and participate in the study, as follows: adult male or female aged 18 years or more on the day of signing the icf, confirmed by identification cards. verified, documentation of past covid-19 vaccination i. study part a: having completed the 2-dose homologous primary regimen (21 to 28 days apart) of inactivated covid-19 vaccine of either sinovac-sinovac or sinopharm-sinopharm ii. study part b: having received one dose of inactivated covid-19 vaccine of either sinovac or sinopharm with the appropriate interval period subject has provided written informed consent prior to performance of any study-specific procedures and is willing and has means to be contacted and to contact the investigator during the study. in the investigator's clinical judgment, the participant is in good health, or has stable and well-controlled medical conditions. participant agrees to not donate bone marrow, blood, and blood products from the study vaccine administration until 3 months after receiving the study vaccine.

inclusion criteria: potential participants must meet all inclusion criteria to be enrolled and participate in the study, as follows: 1. adult male or female aged 18 years or more on the day of signing the icf, confirmed by identification cards. 2. verified, documentation of past covid-19 vaccination i. study part a: having completed the 2-dose homologous primary regimen (21 to 28 days apart) of inactivated covid-19 vaccine of either sinovac-sinovac or sinopharm-sinopharm ii. study part b: having received one dose of inactivated covid-19 vaccine of either sinovac or sinopharm with the appropriate interval period 3. subject has provided written informed consent prior to performance of any study-specific procedures and is willing and has means to be contacted and to contact the investigator during the study. 4. in the investigator's clinical judgment, the participant is in good health, or has stable and well-controlled medical conditions. 5. participant agrees to not donate bone marrow, blood, and blood products from the study vaccine administration until 3 months after receiving the study vaccine.

inclusion criteria: potential participants must meet all inclusion criteria to be enrolled and participate in the study, as follows: 1. adult male or female aged 18 years or more on the day of signing the icf, confirmed by identification cards. 2. verified, documentation of past covid-19 vaccination i. study part a: having completed the 2-dose homologous primary regimen (21 to 28 days apart) of inactivated covid-19 vaccine of either sinovac-sinovac or sinopharm-sinopharm ii. study part b: having received one dose of inactivated covid-19 vaccine of either sinovac or sinopharm with the appropriate interval period 3. subject has provided written informed consent prior to performance of any study-specific procedures and is willing and has means to be contacted and to contact the investigator during the study. 4. in the investigator's clinical judgment, the participant is in good health, or has stable and well-controlled medical conditions. 5. participant agrees to not donate bone marrow, blood, and blood products from the study vaccine administration until 3 months after receiving the study vaccine.