1.Healthy adults aged 18 years and above. Both males and females should be included, 2.The subjects shall fully understand the content of the informed consent form and the study procedure of this clinical trial. The subjects shall be voluntary and capable of signing the informed consent form, 3.The subjects shall be able to communicate well with the investigators, as well as understand and comply with the requirements of this study, 4.At risk of infection with or exposure to SARS-CoV-2 or COVID-19 cases due to factors regarding regions, occupations, activities, environment, etc., 5.For female subjects: no child-bearing potential or effective contraceptive measures have been used within 2 weeks before being included in this study with negative pregnancy test results. No child-bearing potential may include: amenorrhea for at least 1 year or surgical sterilization with medical records. Subjects shall voluntarily agree to continue using effective contraceptive measures with their partners through 3 months after completing Dose 2. Effective contraceptive measures include: abstinence or adequate contraceptive measures (e.g., intrauterine or implantable contraceptive devices, oral contraceptives, injectable or embedded contraceptives, sustained-release topical contraceptives, condoms (male), diaphragm, cervical cap, etc.), 6.Healthy subjects or subjects with mild underlying diseases [in a stable state for at least 3 months before enrollment without aggravation (no need for hospitalization or no major adjustment of treatment plan, etc.)].

1.Healthy adults aged 18 years and above. Both males and females should be included, 2.The subjects shall fully understand the content of the informed consent form and the study procedure of this clinical trial. The subjects shall be voluntary and capable of signing the informed consent form, 3.The subjects shall be able to communicate well with the investigators, as well as understand and comply with the requirements of this study, 4.At risk of infection with or exposure to SARS-CoV-2 or COVID-19 cases due to factors regarding regions, occupations, activities, environment, etc., 5.For female subjects: no child-bearing potential or effective contraceptive measures have been used within 2 weeks before being included in this study with negative pregnancy test results. No child-bearing potential may include: amenorrhea for at least 1 year or surgical sterilization with medical records. Subjects shall voluntarily agree to continue using effective contraceptive measures with their partners through 3 months after completing Dose 2. Effective contraceptive measures include: abstinence or adequate contraceptive measures (e.g., intrauterine or implantable contraceptive devices, oral contraceptives, injectable or embedded contraceptives, sustained-release topical contraceptives, condoms (male), diaphragm, cervical cap, etc.), 6.Healthy subjects or subjects with mild underlying diseases [in a stable state for at least 3 months before enrollment without aggravation (no need for hospitalization or no major adjustment of treatment plan, etc.)].

All subjects are required to meet all the following inclusion criteria: 1. Healthy adults aged 18 years and above. Both males and females should be included, 2. The subjects shall fully understand the content of the informed consent form and the study procedure of this clinical trial. The subjects shall be voluntary and capable of signing the informed consent form, 3. The subjects shall be able to communicate well with the investigators, as well as understand and comply with the requirements of this study, 4. At risk of infection with or exposure to SARS-CoV-2 or COVID-19 cases due to factors regarding regions, occupations, activities, environment, etc., 5. For female subjects: no child-bearing potential or effective contraceptive measures have been used within 2 weeks before being included in this study with negative pregnancy test results. No child-bearing potential may include: amenorrhea for at least 1 year or surgical sterilization with medical records. Subjects shall voluntarily agree to continue using effective contraceptive measures with their partners through 3 months after completing Dose 2. Effective contraceptive measures include: abstinence or adequate contraceptive measures (e.g., intrauterine or implantable contraceptive devices, oral contraceptives, injectable or embedded contraceptives, sustained-release topical contraceptives, condoms (male), diaphragm, cervical cap, etc.), 6. Healthy subjects or subjects with mild underlying diseases [in a stable state for at least 3 months before enrollment without aggravation (no need for hospitalization or no major adjustment of treatment plan, etc.)].

All subjects are required to meet all the following inclusion criteria: 1. Healthy adults aged 18 years and above. Both males and females should be included, 2. The subjects shall fully understand the content of the informed consent form and the study procedure of this clinical trial. The subjects shall be voluntary and capable of signing the informed consent form, 3. The subjects shall be able to communicate well with the investigators, as well as understand and comply with the requirements of this study, 4. At risk of infection with or exposure to SARS-CoV-2 or COVID-19 cases due to factors regarding regions, occupations, activities, environment, etc., 5. For female subjects: no child-bearing potential or effective contraceptive measures have been used within 2 weeks before being included in this study with negative pregnancy test results. No child-bearing potential may include: amenorrhea for at least 1 year or surgical sterilization with medical records. Subjects shall voluntarily agree to continue using effective contraceptive measures with their partners through 3 months after completing Dose 2. Effective contraceptive measures include: abstinence or adequate contraceptive measures (e.g., intrauterine or implantable contraceptive devices, oral contraceptives, injectable or embedded contraceptives, sustained-release topical contraceptives, condoms (male), diaphragm, cervical cap, etc.), 6. Healthy subjects or subjects with mild underlying diseases [in a stable state for at least 3 months before enrollment without aggravation (no need for hospitalization or no major adjustment of treatment plan, etc.)].