inclusion criteria: 1. adults aged 18 years and older. 2. understand the contents of the icf and voluntarily sign it (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 study requirements, including all scheduled visits, vaccinations, laboratory tests, and other study procedures. 4. female participants of childbearing potential or partners of male participants: voluntarily agree to use effective contraception with their partners 14 days prior to the vaccination and must agree to continue such precautions during the study until 3 months after vaccination. \[effective contraception includes oral contraceptives, injectable or implantable contraception, extended-release topical contraceptives, hormonal patches, intrauterine devices (iuds), sterilization, abstinence, condoms (for males), diaphragms, cervical caps, etc.\]. 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 vaccination in this study. 6. axillary temperature \<37.3°c/99.1°f at screening visit and 72 hours prior to vaccination. 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 vaccinated 2 doses of coronavac® (with an interval of 3-8 weeks between 2 doses), for 6-12 months prior to enrollment.

inclusion criteria: 1. adults aged 18 years and older. 2. understand the contents of the icf and voluntarily sign it (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 study requirements, including all scheduled visits, vaccinations, laboratory tests, and other study procedures. 4. female participants of childbearing potential or partners of male participants: voluntarily agree to use effective contraception with their partners 14 days prior to the vaccination and must agree to continue such precautions during the study until 3 months after vaccination. \[effective contraception includes oral contraceptives, injectable or implantable contraception, extended-release topical contraceptives, hormonal patches, intrauterine devices (iuds), sterilization, abstinence, condoms (for males), diaphragms, cervical caps, etc.\]. 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 vaccination in this study. 6. axillary temperature \<37.3°c/99.1°f at screening visit and 72 hours prior to vaccination. 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 vaccinated 2 doses of coronavac® (with an interval of 3-8 weeks between 2 doses), for 6-12 months prior to enrollment.

inclusion criteria: adults aged 18 years and older. understand the contents of the icf and voluntarily sign it (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 study requirements, including all scheduled visits, vaccinations, laboratory tests, and other study procedures. female participants of childbearing potential or partners of male participants: voluntarily agree to use effective contraception with their partners 14 days prior to the vaccination and must agree to continue such precautions during the study until 3 months after vaccination. [effective contraception includes oral contraceptives, injectable or implantable contraception, extended-release topical contraceptives, hormonal patches, intrauterine devices (iuds), sterilization, abstinence, condoms (for males), 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 vaccination in this study. axillary temperature <37.3°c/99.1°f at screening visit and 72 hours prior to vaccination. 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 vaccinated 2 doses of coronavac® (with an interval of 3-8 weeks between 2 doses), for 6-12 months prior to enrollment.

inclusion criteria: adults aged 18 years and older. understand the contents of the icf and voluntarily sign it (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 study requirements, including all scheduled visits, vaccinations, laboratory tests, and other study procedures. female participants of childbearing potential or partners of male participants: voluntarily agree to use effective contraception with their partners 14 days prior to the vaccination and must agree to continue such precautions during the study until 3 months after vaccination. [effective contraception includes oral contraceptives, injectable or implantable contraception, extended-release topical contraceptives, hormonal patches, intrauterine devices (iuds), sterilization, abstinence, condoms (for males), 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 vaccination in this study. axillary temperature <37.3°c/99.1°f at screening visit and 72 hours prior to vaccination. 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 vaccinated 2 doses of coronavac® (with an interval of 3-8 weeks between 2 doses), for 6-12 months prior to enrollment.