inclusion criteria: * the subjects must meet all of the following inclusion criteria (phase i): 1. voluntarily sign the icf approved by the ethics committee before any study procedure and agree to participate in the study. 2. healthy male or female able to provide legal identity certificate and aged 18 years and older when signing the icf. 3. subjects who are fully vaccinated either by 2 or 3 doses. the 2-dose immunization or the second dose of the 3-dose immunization should be from 6 to 24 months before administration of the investigational vaccine. the third dose should be \>3 months before administration of the investigational vaccine. 4. be able to communicate well with the investigator, and to understand and comply with the requirements of this clinical trial. 5. males and females with childbearing potential voluntarily take effective contraceptive methods from signing icf to 3 months after completing 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).

inclusion criteria: * the subjects must meet all of the following inclusion criteria (phase i): 1. voluntarily sign the icf approved by the ethics committee before any study procedure and agree to participate in the study. 2. healthy male or female able to provide legal identity certificate and aged 18 years and older when signing the icf. 3. subjects who are fully vaccinated either by 2 or 3 doses. the 2-dose immunization or the second dose of the 3-dose immunization should be from 6 to 24 months before administration of the investigational vaccine. the third dose should be \>3 months before administration of the investigational vaccine. 4. be able to communicate well with the investigator, and to understand and comply with the requirements of this clinical trial. 5. males and females with childbearing potential voluntarily take effective contraceptive methods from signing icf to 3 months after completing 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).

inclusion criteria: the subjects must meet all of the following inclusion criteria (phase i): voluntarily sign the icf approved by the ethics committee before any study procedure and agree to participate in the study. healthy male or female able to provide legal identity certificate and aged 18 years and older when signing the icf. subjects who are fully vaccinated either by 2 or 3 doses. the 2-dose immunization or the second dose of the 3-dose immunization should be from 6 to 24 months before administration of the investigational vaccine. the third dose should be >3 months before administration of the investigational vaccine. be able to communicate well with the investigator, and to understand and comply with the requirements of this clinical trial. males and females with childbearing potential voluntarily take effective contraceptive methods from signing icf to 3 months after completing 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).

inclusion criteria: the subjects must meet all of the following inclusion criteria (phase i): voluntarily sign the icf approved by the ethics committee before any study procedure and agree to participate in the study. healthy male or female able to provide legal identity certificate and aged 18 years and older when signing the icf. subjects who are fully vaccinated either by 2 or 3 doses. the 2-dose immunization or the second dose of the 3-dose immunization should be from 6 to 24 months before administration of the investigational vaccine. the third dose should be >3 months before administration of the investigational vaccine. be able to communicate well with the investigator, and to understand and comply with the requirements of this clinical trial. males and females with childbearing potential voluntarily take effective contraceptive methods from signing icf to 3 months after completing 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).