inclusion criteria: * 1. voluntarily sign the icf approved by the ethics committee and agree to participate in the study before any study procedure. * 2. healthy males or females able to provide legal identification, aged 18 years and above at the time of signing icf. * 3. subjects who have completed homologous primary vaccination with either inactivated or mrna or viral vector covid-19 vaccines (full approval, cma or eua) and have the last dose administered 6 months ago or earlier from the date of signing the icf for the study. those who have received combined immunization with two doses of vaccines should be excluded. * 4. able to communicate well with the investigator, and able to understand and comply with the requirements of this clinical trial. * 5. males with female sexual partners or females of childbearing potential voluntarily take effective contraceptive methods from signing icf to 3 months after the vaccination, including sexual abstinence or effective contraceptive measures (e.g., intrauterine or implanted contraceptive device, oral contraceptives, injected or implanted contraceptives, sustained-release topical contraceptives, intrauterine device (iud), condoms (male), diaphragm, and cervical cap). * 6. axillary temperature \<37.3℃.

inclusion criteria: * 1. voluntarily sign the icf approved by the ethics committee and agree to participate in the study before any study procedure. * 2. healthy males or females able to provide legal identification, aged 18 years and above at the time of signing icf. * 3. subjects who have completed homologous primary vaccination with either inactivated or mrna or viral vector covid-19 vaccines (full approval, cma or eua) and have the last dose administered 6 months ago or earlier from the date of signing the icf for the study. those who have received combined immunization with two doses of vaccines should be excluded. * 4. able to communicate well with the investigator, and able to understand and comply with the requirements of this clinical trial. * 5. males with female sexual partners or females of childbearing potential voluntarily take effective contraceptive methods from signing icf to 3 months after the vaccination, including sexual abstinence or effective contraceptive measures (e.g., intrauterine or implanted contraceptive device, oral contraceptives, injected or implanted contraceptives, sustained-release topical contraceptives, intrauterine device (iud), condoms (male), diaphragm, and cervical cap). * 6. axillary temperature \<37.3℃.

inclusion criteria: 1. voluntarily sign the icf approved by the ethics committee and agree to participate in the study before any study procedure. 2. healthy males or females able to provide legal identification, aged 18 years and above at the time of signing icf. 3. subjects who have completed homologous primary vaccination with either inactivated or mrna or viral vector covid-19 vaccines (full approval, cma or eua) and have the last dose administered 6 months ago or earlier from the date of signing the icf for the study. those who have received combined immunization with two doses of vaccines should be excluded. 4. able to communicate well with the investigator, and able to understand and comply with the requirements of this clinical trial. 5. males with female sexual partners or females of childbearing potential voluntarily take effective contraceptive methods from signing icf to 3 months after the vaccination, including sexual abstinence or effective contraceptive measures (e.g., intrauterine or implanted contraceptive device, oral contraceptives, injected or implanted contraceptives, sustained-release topical contraceptives, intrauterine device (iud), condoms (male), diaphragm, and cervical cap). 6. axillary temperature <37.3℃.

inclusion criteria: 1. voluntarily sign the icf approved by the ethics committee and agree to participate in the study before any study procedure. 2. healthy males or females able to provide legal identification, aged 18 years and above at the time of signing icf. 3. subjects who have completed homologous primary vaccination with either inactivated or mrna or viral vector covid-19 vaccines (full approval, cma or eua) and have the last dose administered 6 months ago or earlier from the date of signing the icf for the study. those who have received combined immunization with two doses of vaccines should be excluded. 4. able to communicate well with the investigator, and able to understand and comply with the requirements of this clinical trial. 5. males with female sexual partners or females of childbearing potential voluntarily take effective contraceptive methods from signing icf to 3 months after the vaccination, including sexual abstinence or effective contraceptive measures (e.g., intrauterine or implanted contraceptive device, oral contraceptives, injected or implanted contraceptives, sustained-release topical contraceptives, intrauterine device (iud), condoms (male), diaphragm, and cervical cap). 6. axillary temperature <37.3℃.