inclusion criteria: 1. adults aged 18 years and older; 2. understand the content of the icf, and voluntarily sign the icf (if the participant is unable to sign the icf on his/her own due to illiteracy, an impartial witness is needed); 3. participants who are willing and able to comply with all scheduled visits, vaccination plan, laboratory tests, lifestyle considerations, and other study procedures; 4. female participants of childbearing potential or partners of male participants: voluntarily agree to use effective contraception with their partners prior to the first vaccination and must agree to continue such precautions during the study until 3 months after booster vaccination \[effective contraception includes oral contraceptives, injectable or implantable contraception, extended-release topical contraceptives, hormonal patches, intrauterine devices (iuds), sterilization, abstinence, condoms (for male), diaphragms, cervical caps, etc.); 5. for female participants: without childbearing potential (amenorrhea for at least 1 year or documented surgical sterilization) or have used effective contraception with a negative pregnancy test before booster vaccination in this study； 6. on the day of vaccination and 24 hours prior to vaccination, axillary temperatures\<37.3°c/99.1°f; 7. healthy participants or participants with mild underlying disease \[in a stable state without exacerbation (no admission to hospital or no major adjustment to treatment regimen, etc.) for at least 3 months prior to enrollment in this study\]; 8. participants who have received primary/1 booster dose(s) of sars-cov-2 vaccination (including primary series of inactivated vaccine, mrna vaccine, adenovirus vaccine or 1 homologous/heterologous booster), with the last dose received at least 6 months before enrolment. documented confirmation of prior sars-cov-2 vaccination receipt must be obtained prior to randomization;

inclusion criteria: 1. adults aged 18 years and older; 2. understand the content of the icf, and voluntarily sign the icf (if the participant is unable to sign the icf on his/her own due to illiteracy, an impartial witness is needed); 3. participants who are willing and able to comply with all scheduled visits, vaccination plan, laboratory tests, lifestyle considerations, and other study procedures; 4. female participants of childbearing potential or partners of male participants: voluntarily agree to use effective contraception with their partners prior to the first vaccination and must agree to continue such precautions during the study until 3 months after booster vaccination \[effective contraception includes oral contraceptives, injectable or implantable contraception, extended-release topical contraceptives, hormonal patches, intrauterine devices (iuds), sterilization, abstinence, condoms (for male), diaphragms, cervical caps, etc.); 5. for female participants: without childbearing potential (amenorrhea for at least 1 year or documented surgical sterilization) or have used effective contraception with a negative pregnancy test before booster vaccination in this study； 6. on the day of vaccination and 24 hours prior to vaccination, axillary temperatures\<37.3°c/99.1°f; 7. healthy participants or participants with mild underlying disease \[in a stable state without exacerbation (no admission to hospital or no major adjustment to treatment regimen, etc.) for at least 3 months prior to enrollment in this study\]; 8. participants who have received primary/1 booster dose(s) of sars-cov-2 vaccination (including primary series of inactivated vaccine, mrna vaccine, adenovirus vaccine or 1 homologous/heterologous booster), with the last dose received at least 6 months before enrolment. documented confirmation of prior sars-cov-2 vaccination receipt must be obtained prior to randomization;

inclusion criteria: adults aged 18 years and older; understand the content of the icf, and voluntarily sign the icf (if the participant is unable to sign the icf on his/her own due to illiteracy, an impartial witness is needed); participants who are willing and able to comply with all scheduled visits, vaccination plan, laboratory tests, lifestyle considerations, and other study procedures; female participants of childbearing potential or partners of male participants: voluntarily agree to use effective contraception with their partners prior to the first vaccination and must agree to continue such precautions during the study until 3 months after booster vaccination [effective contraception includes oral contraceptives, injectable or implantable contraception, extended-release topical contraceptives, hormonal patches, intrauterine devices (iuds), sterilization, abstinence, condoms (for male), diaphragms, cervical caps, etc.); for female participants: without childbearing potential (amenorrhea for at least 1 year or documented surgical sterilization) or have used effective contraception with a negative pregnancy test before booster vaccination in this study； on the day of vaccination and 24 hours prior to vaccination, axillary temperatures<37.3°c/99.1°f; healthy participants or participants with mild underlying disease [in a stable state without exacerbation (no admission to hospital or no major adjustment to treatment regimen, etc.) for at least 3 months prior to enrollment in this study]; participants who have received primary/1 booster dose(s) of sars-cov-2 vaccination (including primary series of inactivated vaccine, mrna vaccine, adenovirus vaccine or 1 homologous/heterologous booster), with the last dose received at least 6 months before enrolment. documented confirmation of prior sars-cov-2 vaccination receipt must be obtained prior to randomization;

inclusion criteria: adults aged 18 years and older; understand the content of the icf, and voluntarily sign the icf (if the participant is unable to sign the icf on his/her own due to illiteracy, an impartial witness is needed); participants who are willing and able to comply with all scheduled visits, vaccination plan, laboratory tests, lifestyle considerations, and other study procedures; female participants of childbearing potential or partners of male participants: voluntarily agree to use effective contraception with their partners prior to the first vaccination and must agree to continue such precautions during the study until 3 months after booster vaccination [effective contraception includes oral contraceptives, injectable or implantable contraception, extended-release topical contraceptives, hormonal patches, intrauterine devices (iuds), sterilization, abstinence, condoms (for male), diaphragms, cervical caps, etc.); for female participants: without childbearing potential (amenorrhea for at least 1 year or documented surgical sterilization) or have used effective contraception with a negative pregnancy test before booster vaccination in this study； on the day of vaccination and 24 hours prior to vaccination, axillary temperatures<37.3°c/99.1°f; healthy participants or participants with mild underlying disease [in a stable state without exacerbation (no admission to hospital or no major adjustment to treatment regimen, etc.) for at least 3 months prior to enrollment in this study]; participants who have received primary/1 booster dose(s) of sars-cov-2 vaccination (including primary series of inactivated vaccine, mrna vaccine, adenovirus vaccine or 1 homologous/heterologous booster), with the last dose received at least 6 months before enrolment. documented confirmation of prior sars-cov-2 vaccination receipt must be obtained prior to randomization;