Inclusion Criteria:

1. Both male and female adults aged 18 and above who can provide identification;

2. Know the contents of the informed consent form and the situation of the vaccination,
sign the informed consent form voluntarily, and have the ability to use the
thermometer, scale and fill in the diary card and contact card as required;

3. Ability to communicate well with researchers, understand and comply with the
requirements of the study;

4. Two or three doses of COVID-19 inactivated vaccine have been completed and ≥6 months
have passed since the last dose of COVID-19 inactivated vaccine;

5. Healthy subjects or subjects with mild underlying diseases [stable condition with no
worsening condition (no need for hospitalization or no major adjustment in treatment
regimen, etc.) for at least 3 months prior to inclusion in the study];

6. Women who are not possibility to have children (amenorrhea for at least 1 year or
surgical sterilization with medical records) or who are known not to be pregnant or
lactating and who have used effective contraception for nearly 14 days before
vaccination (e.g., Intrauterine or implantable contraceptive devices,oral
contraceptives, injected or embedded contraceptives, slow-release topical
contraceptives, intrauterine devices (IUD), condoms (male), diaphragm, cervical cap,
etc.) (provide negative proof of pregnancy within 48 hours);

7. SARS-CoV-2 etiology test (RT-PCR) was negative within 48 hours.

Exclusion Criteria:

1. Abnormal vital signs that are clinically significant (e.g. abnormal controlled blood
pressure);

2. Have been infected with COVID-19 or used any COVID-19 prophylactic medication other
than 3 doses of COVID-19 inactivated vaccine within the last 6 months (for example,
a history of any other non-COVID-19 inactivated vaccine on or off the market, or 1
or 4 doses of COVID-19 inactivated vaccine);

3. History of severe acute respiratory syndrome (SARS), Middle East Respiratory
Syndrome (MERS) and other human coronavirus infection or disease history;

4. Axillary temperature ≥37.3℃ or fever within 24 hours on the day of vaccination
(axillary temperature ≥37.3℃/ mouth temperature ≥37.5℃);

5. A history of severe allergic reactions or allergic reactions to vaccines or drugs,
such as urticaria, severe eczema, dyspnea, laryngeal edema, angioneurotic edema,
etc.;

6. Vaccination of any vaccine within 28 days prior to study vaccination;

7. Enrolled in a clinical study of another drug within 28 days before vaccination or
planned to participate in a clinical study of another drug within 6 months after
vaccination;

8. Have a genetic tendency to bleed or abnormal coagulation function (e.g. cytokine
deficiency, coagulation disorder or thrombocytopenia), or a history of severe
bleeding;

9. A known history or diagnosis of a disease affecting immune system function, such as
cancer (other than basal cell carcinoma of the skin), congenital or acquired
immunodeficiency (e.g., HIV infection), uncontrolled autoimmune disease, etc.;

10. Asplenia or functional asplenia;

11. Long-term use (continuous use ≥14 days) of immunosuppressants or other
immunomodulatory drugs (e.g., cortisol: prednisone or similar drugs) within 6 months
prior to study vaccination; Interferon, etc.), but topical use (such as ointments,
eye drops, inhalants or nasal sprays) is permitted, and the dose of topical use
shall not exceed that recommended in the instructions;

12. Received immunoglobulin and/or blood products within 3 months prior to study
vaccination;

13. Suspected or known alcohol dependence or drug abuse;

14. Other factors considered inappropriate to be included in the study.