Inclusion Criteria:

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1. Voluntarily sign the ICF approved by the Ethics Committee and agree to
participate in the study before any study procedure.

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2. Healthy males or females able to provide legal identification, aged 18 years
and above at the time of signing ICF.

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3. Subjects who have completed homologous primary vaccination with either
Inactivated or mRNA or Viral Vector COVID-19 vaccines (full approval, CMA or
EUA) and have the last dose administered 6 months ago or earlier from the date
of signing the ICF for the study. Those who have received combined immunization
with two doses of vaccines should be excluded.

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4. Able to communicate well with the investigator, and able to understand and
comply with the requirements of this clinical trial.

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5. Males with female sexual partners or females of childbearing potential
voluntarily take effective contraceptive methods from signing ICF to 3 months
after 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).

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6. Axillary temperature <37.3℃.

Exclusion Criteria:

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1. Positive SARS-CoV-2 RT-PCR at screening.

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2. Prior medical history of Serve Acute Respiratory Syndromes (SARS), Middle East
Respiratory Syndrome (MERS) and other human coronavirus infections or diseases.

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3. Prior history or family history of convulsion, epilepsy, encephalopathy and
psychosis.

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4. Fear of needles.

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5. Pregnant or lactating females or those who plan to become pregnant or donate
eggs during study period.

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6. Prior history of allergic reaction or anaphylaxis to any vaccine or its
excipients, e.g., hypersensitivity, urticaria, serious eczema, dyspnea,
laryngeal edema, and angioedema etc..

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7. Prior use of any vaccine within 28 days before receiving this investigational
vaccine or planning to use any vaccine other than this investigational vaccine
during the study period.

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8. Participation in studies of any other interventional device or drug within 28
days before the screening, or current treatment with other investigational
drug(s) or within 5 half-lives after taking the last dose of the study drug.

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9. Hereditary hemorrhagic tendency or coagulation dysfunction (e.g., clotting
factors deficiency, coagulation disorders or platelet disorders), or a history
of severe bleeding, or a history of massive bleeding after intramuscular
injection or venipuncture, or a history of ecchymosis.

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10. Known medical history or diagnosis confirming that subjects have diseases
affecting immune system function, including cancer, congenital or acquired
immunodeficiency (e.g., infection with Human Immunodeficiency Virus (HIV)), or
uncontrolled autoimmune disease.

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11. Serious or uncontrolled respiratory system disorders, cardiovascular disorders,
nervous system disorders, blood and lymphatic system disorders, liver and
kidney disorders, metabolism and skeletal disorders, etc. influencing study
results evaluation at the investigator's discretion.

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12. Asplenia or functional asplenia.

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13. Long-term use (continuous use for ≥14 days) of immunosuppressants or other
immunomodulators (e.g., glucocorticoids: prednisone or equivalents) within 6
months prior to administration of this investigational vaccine, except for
topical medications (e.g., ointments, eye drops, inhalants or nasal sprays).
And the topical medications should not exceed the recommended dose in the
labels or induce any signs of systemic exposure.

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14. Having received immunoglobulins and/or blood products within 3 months prior to
administration of this investigational vaccine.

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15. History of tuberculosis treatment or currently on antikoch's treatment for
tuberculosis, whether pulmonary or extrapulmonary.

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16. Suspected or known alcohol dependency or drug abuse, which may affect safety
evaluation or subject's compliance at the investigator's discretion.

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17. Planning to permanently move from the local area before study completion or
leave the local area for a long time during the period of study visits.

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18. An employee of the study site, Sponsor and contract research organization (CRO)
taking part in the study.

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19. Other conditions unsuitable for this study at the investigator's discretion.