Inclusion Criteria:

- Adults aged 18 years and older.

- 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).

- Participants who are willing and able to comply with all scheduled visits,
vaccination plan, laboratory tests, lifestyle considerations, and other study
procedures.

- Female participants of childbearing potential or partners of male participants:
voluntarily agree to use effective contraception with their partners prior to the
(1st dose of) vaccination and must agree to continue such precautions during the
study until 3 months after (full) 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.].

- 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 dose of) vaccination in this study.

- On the day of vaccination and 24 hours prior to (each dose of) vaccination, axillary
temperatures<37.3℃/99.1°F.

- 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].

- (For group 2 and group 3 only) Participants who have received full primary
vaccination of licensed SARS-CoV-2 vaccine (3-8 weeks between 2 doses of COVID-19
inactivated vaccine or 2 doses of COVID-19 mRNA vaccine) and whose last dose was
given >6 mony

- (For group 1 only) Not have received any COVID-19 vaccine prior to enrollment.

Exclusion Criteria:

- Any screening hematology and/or blood biochemistry laboratory value that meets the
definition of a ≥Grade 1 abnormality,

- (For group 1 only) Confirmed SARS-CoV-2 diagnosis within 1 years before screening
visit.

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

- Receipt of medications intended to treat COVID-19 with 1 year.

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

- SARS-CoV-2 RT-PCR positive nasopharyngeal/oropharyngeal swab specimens at screening.

- Positive HIV test at screening.

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

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

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

- 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.

- Any other licensed vaccines given within 28 days prior to the investigational
vaccination, or planned administration of vaccine(s) within 28 days after (full)
vaccination.

- Receipt of blood/plasma products, immunoglobulin, or monoclonal antibodies, form 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.

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

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

- Women who are pregnant or breastfeeding.

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

- (For group 1 only: Criteria for delay of 2nd dose of vaccination) Fever within 24
hours prior to the 2nd dose of vaccination (axillary body temperature
≥37.3℃/99.1°F).

- (For group 1 only: Criteria for delay of 2nd dose of vaccination) During
treatment/recovery from illness.

- (For group 1 only: Criteria for delay of 2nd dose of vaccination) Other conditions
considered by the investigator to be unsuitable for vaccination.

- (For group 1 only: Criteria for termination of 2nd dose of vaccination) Participants
with a positive urine pregnancy or blood pregnancy test (women of childbearing age
only).

- (For group 1 only: Criteria for termination of 2nd dose of vaccination) Serious
allergic reactions or serious adverse events related to vaccination (as assessed by
the investigator) following a previous dose of vaccine.

- (For group 1 only: Criteria for termination of 2nd dose of vaccination) Positive
result for SARS-CoV-2 (positive RT-PCR test).

- (For group 1 only: Criteria for termination of 2nd dose of vaccination) The
investigator considers inappropriate for the participants to continue participation
in the study.