Inclusion Criteria:

1. Adults aged 18 years and older.

2. Understand the content of the Informed Consent Form (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 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 prior to the
first vaccination and must agree to continue such precautions during the study until
3 months after full vaccination (including the initial set of vaccination and
crossover set of 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 each vaccination in this study.

6. On the day of 1st dose 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].

Exclusion Criteria:

1. History of Severe Acute Respiratory Syndrome (SARS), Middle East Respiratory
Syndrome (MERS), or other coronavirus infections.

2. Individuals using prescription medications for prophylaxis or treatment of
SARS-CoV-2 (including vaccination of licensed COVID-19 vaccines).

3. History of a previous laboratory-confirmed diagnosis of SARS-CoV-2 infection or
COVID-19.

4. History of allergy to any component of the study vaccine or history of severe
allergic reaction to vaccine or drug (including but not limited to anaphylaxis,
allergic laryngeal edema, anaphylactic purpura, thrombocytopenic purpura, or
localized allergic necrosis (Arthus reaction)).

5. Positive nucleic acid for SARS-CoV-2 in nasopharyngeal/oropharyngeal swab specimens.

6. Positive HIV test results.

7. A history or family history of convulsions, epilepsy, encephalopathy and psychosis.

8. Malignant tumors in the active phase, malignant tumors not receiving adequate
treatment, malignant tumors at potential risk of recurrence during the study period.

9. Asplenia or functional asplenia, complete or partial splenectomy from any cause.

10. Prolonged (defined as more than 14 days) use of immunosuppressive or other
immunomodulatory drugs (e.g., corticosteroids, ≥20 mg/d prednisone or equivalent;
however, inhaled and topical steroids are permitted) within 6 months prior to the
1st dose of investigational vaccine.

11. Any other licensed vaccines given within 28 days prior to the study vaccination, or
planned administration of vaccine(s) within 28 days after the 2nd dose in the
blinded crossover vaccination.

12. Have received immunoglobulin or other blood products within 3 months prior to
enrollment or plan to receive them during the study period.

13. Blood donation or blood loss ≥ 450 mL within 1 month prior to enrollment or planned
to donate blood during the study period.

14. Participants who have received any other investigational product within 1 month
prior to enrollment or intent to participate in another clinical study at any time
during the conduct of this study.

15. Women who are pregnant or breastfeeding.

16. Participants deemed unsuitable for participation in this study based on the
investigator's assessment.