Inclusion Criteria:

1. Adults aged 18 years and older;

2. Understand the content of the 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 all scheduled visits,
vaccination plan, laboratory tests, lifestyle considerations, 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 booster 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 booster vaccination in this study；

6. On the day 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];

8. Participants who have received primary/1 booster dose(s) of SARS-CoV-2 vaccination
(including primary series of inactivated vaccine, mRNA vaccine, adenovirus vaccine
or 1 homologous/heterologous booster), with the last dose received at least 6 months
before enrolment. Documented confirmation of prior SARS-CoV-2 vaccination receipt
must be obtained prior to randomization;

Exclusion Criteria:

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

2. History of hepatitis A, hepatitis B, hepatitis C, syphilis infection based on
medical inquiry.;

3. History of severe adverse reaction associated with a vaccine or drug and/or severe
allergic reaction (e.g., anaphylaxis) to any component of the study intervention(s);

4. Receipt of medications intended to treat COVID-19 within 6 months;

5. Virologically confirmed SARS-CoV-2 diagnosis within 6 months before screening visit;

6. Positive nasopharyngeal/oropharyngeal swab SARS-CoV-2 RT-PCR test result at
screening;

7. Positive HIV test result at screening;

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

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

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

11. Individuals who receive treatment with radiotherapy or immunosuppressive therapy,
including cytotoxic agents or systemic corticosteroids (if systemic corticosteroids
are administered for ≥14 days at a dose of ≥20 mg/day of prednisone or equivalent),
e.g., for cancer or an autoimmune disease, or planned receipt throughout the study.
Inhaled/nebulized, intra-articular, epidural, or topical (skin or eyes)
corticosteroids are permitted;

12. Any other licensed vaccines given within 28 days prior to vaccination, planned
administration of any other vaccines within 28 days after vaccination, or planned
administration of other COVID-19 vaccines during the entire study duration;

13. Receipt of blood/plasma products, immunoglobulin, or monoclonal antibodies, from 60
days before vaccine administration, or receipt of any passive antibody therapy
specific to COVID-19, from 90 days before vaccine administration, or planned receipt
throughout the study;

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

15. Participation in other studies involving study intervention within 28 days prior to
study entry, and/or during the study;

16. Women who are pregnant or breastfeeding;

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