inclusion criteria: 1. healthy subjects aged 18-59 years, including both males and females; 2. subjects who agree to participate in this clinical trial voluntarily and sign the informed consent form, are capable of providing valid identification, understanding and complying with the requirements of the clinical protocol. 3. subjects who have completed three-dose inactivated covid-19 vaccine at 6 months earlier; 4. s-protein binding antibody igg concentration was less than 300bau/ml before booster vaccination in cohort 1, while s-protein binding antibody igg concentration was not screened in cohort 2; subjects in cohort 1 and cohort 2 were negative in nucleic acid test or antigen test before booster vaccination. 5. for female participants of childbearing potential, effective contraception measures should be used within 2 weeks prior to participation in this study and the results of pregnancy test is required to be negative. participants should voluntarily agree to use effective contraceptive measures from the time of signing the informed consent form to the end of the study (effective contraceptive measures including oral contraceptives (excluding emergency contraceptives), injectable or implantable contraceptives, sustained-release topical contraceptives, hormonal patches, intrauterine device, sterilization, abstinence, condoms (for males), diaphragms, cervical caps, etc.).

inclusion criteria: 1. healthy subjects aged 18-59 years, including both males and females; 2. subjects who agree to participate in this clinical trial voluntarily and sign the informed consent form, are capable of providing valid identification, understanding and complying with the requirements of the clinical protocol. 3. subjects who have completed three-dose inactivated covid-19 vaccine at 6 months earlier; 4. s-protein binding antibody igg concentration was less than 300bau/ml before booster vaccination in cohort 1, while s-protein binding antibody igg concentration was not screened in cohort 2; subjects in cohort 1 and cohort 2 were negative in nucleic acid test or antigen test before booster vaccination. 5. for female participants of childbearing potential, effective contraception measures should be used within 2 weeks prior to participation in this study and the results of pregnancy test is required to be negative. participants should voluntarily agree to use effective contraceptive measures from the time of signing the informed consent form to the end of the study (effective contraceptive measures including oral contraceptives (excluding emergency contraceptives), injectable or implantable contraceptives, sustained-release topical contraceptives, hormonal patches, intrauterine device, sterilization, abstinence, condoms (for males), diaphragms, cervical caps, etc.).

inclusion criteria: healthy subjects aged 18-59 years, including both males and females; subjects who agree to participate in this clinical trial voluntarily and sign the informed consent form, are capable of providing valid identification, understanding and complying with the requirements of the clinical protocol. subjects who have completed three-dose inactivated covid-19 vaccine at 6 months earlier; s-protein binding antibody igg concentration was less than 300bau/ml before booster vaccination in cohort 1, while s-protein binding antibody igg concentration was not screened in cohort 2; subjects in cohort 1 and cohort 2 were negative in nucleic acid test or antigen test before booster vaccination. for female participants of childbearing potential, effective contraception measures should be used within 2 weeks prior to participation in this study and the results of pregnancy test is required to be negative. participants should voluntarily agree to use effective contraceptive measures from the time of signing the informed consent form to the end of the study (effective contraceptive measures including oral contraceptives (excluding emergency contraceptives), injectable or implantable contraceptives, sustained-release topical contraceptives, hormonal patches, intrauterine device, sterilization, abstinence, condoms (for males), diaphragms, cervical caps, etc.).

inclusion criteria: healthy subjects aged 18-59 years, including both males and females; subjects who agree to participate in this clinical trial voluntarily and sign the informed consent form, are capable of providing valid identification, understanding and complying with the requirements of the clinical protocol. subjects who have completed three-dose inactivated covid-19 vaccine at 6 months earlier; s-protein binding antibody igg concentration was less than 300bau/ml before booster vaccination in cohort 1, while s-protein binding antibody igg concentration was not screened in cohort 2; subjects in cohort 1 and cohort 2 were negative in nucleic acid test or antigen test before booster vaccination. for female participants of childbearing potential, effective contraception measures should be used within 2 weeks prior to participation in this study and the results of pregnancy test is required to be negative. participants should voluntarily agree to use effective contraceptive measures from the time of signing the informed consent form to the end of the study (effective contraceptive measures including oral contraceptives (excluding emergency contraceptives), injectable or implantable contraceptives, sustained-release topical contraceptives, hormonal patches, intrauterine device, sterilization, abstinence, condoms (for males), diaphragms, cervical caps, etc.).