Inclusion Criteria:

- 18 years old and above adults.

- Able and willing to comply with the requirements of the clinical trial protocol and
able to sign the informed consent form.

- Willing to discuss medical history with the investigator or physician and allow
access to all medical records related to this trial.

Subjects have completed 3 doses of inactivated vaccine with at least 6 months between the
last dose.

Exclusion Criteria:

- Subject is unfit to participate in the study based on the investigator's judgment.

- History of Middle East Respiratory Syndrome (MERS), Severe Acute Respiratory
Syndrome(SARS) or other coronavirus infection or disease or history of related
immunizations.

- Prior history of severe allergic reactions or hypersensitivity to vaccines or drugs,
such as urticaria, severe skin eczema, dyspnea, laryngeal edema, hemangioma, etc.,
or history of serious adverse reactions associated with vaccines and/or history of
severe anaphylactic reactions (e.g., systemic allergic reactions) to any component
of the study vaccine.

- Immunocompromised individuals with known or suspected immunodeficiency as determined
by medical history and/or physical examination, inability to control autoimmune
disease, etc.

- Bleeding constitutional or condition associated with prolonged bleeding, which the
investigator believes is contraindicated by intramuscular injection.

- Positive urine pregnancy test or lactating women, volunteers or their partners who
have plans to become pregnant within 6 months.

- Severe hypertension and uncontrolled by medication (at the time of field
measurement: systolic blood pressure ≥ 160 mmHg and diastolic blood pressure ≥ 100
mmHg).

- Suffering from a serious chronic disease or in a progressive stage that cannot be
controlled smoothly, such as severe diabetes mellitus, thyroid disease, etc.

- Previously suffering from serious cardiac diseases such as myocarditis and
pericarditis.

- Those who have planned to receive other vaccines within 28 days before or after the
trial vaccination.

- Those receiving immunosuppressive therapy, including cytotoxic drugs or systemic
corticosteroids, such as treatment for cancer or autoimmune disease, or are
scheduled to receive treatment throughout the study period. If systemic
corticosteroids are used for a short period of time (<14 days) for the treatment of
an acute disease, subjects should not be allowed to enter this study until at least
28 days after corticosteroid therapy has ceased prior to study vaccination.
Inhalation/spray, intra-articular, intra-bone, or topical (skin or eye)
corticosteroid use is permitted.

- Have received or plan to receive blood/plasma products or immunoglobulins throughout
the study period 60 days prior to study inoculation.

- Participated in other studies involving interventional studies within 28 days prior
to study entry and/or during study participation.

- Have participated in other interventional studies involving lipid-containing
nanoparticles.

- Have suspected COVID-19 symptoms such as respiratory symptoms, fever, cough,
shortness of breath, and dyspnea.

- Axillary temperature >37.0°C or use of over-the-counter medications such as
antipyretics and analgesics (e.g. acetaminophen, ibuprofen, naproxen, etc.) within
12 hours prior to experimental vaccination.