Inclusion Criteria:

- Age range: populations aged 18 years and above.

- Judged by the investigator that the health condition is well after inquiry and
physical examination.

- Vaccinated with 2 doses/3 doses of inactivated COVID-19 vaccine or mRNA vaccine for
≥ 3 months.

- Female participants who are not nursing or pregnant at the time of enrolment
(negative urine pregnancy test) and have no family planning within the first 7
months after enrollment. Effective contraceptive measures have been taken within 2
weeks before inclusion.

- During the whole follow-up period of the study, be able and willing to complete the
whole prescribed study plan.

- With self ability to understand the study procedures, the informed consent &
voluntarily sign an informed consent form and is able to comply with the
requirements of the clinical study protocol.

Exclusion Criteria:

- Confirmed cases, suspected cases or asymptomatic cases of COVID-19;

- With a history of Severe Acute Respiratory Syndrome (SARS) and Middle East
Respiratory Syndrome (MERS) (self-report, on-site inquiry);

- Has vaccinated with one or four doses and above COVID-19 vaccine;

- Axillary temperature ≥37.3℃ (Tympanic temperature ≥ 37.6 ℃);

- Previous allergic reactions to drug or vaccination (such as acute allergic
reactions, urticaria, eczema, dyspnea, angioneurotic edema or abdominal pain) or
allergy to known components of COVID-19 vaccine (self-report, onsite enquiry);

- Have a history of hospital-diagnosed thrombocytopenia or other coagulation disorders
(self-report, onsite enquiry);

- With known immunological impairment or immunocompromised diagnosed by the hospital
(self-report, onsite enquiry);

- Have an uncontrolled epilepsy and other progressive neurological diseases or a
history of Guillain-Barre syndrome (self-report, onsite enquiry);

- Received whole blood, plasma and immunoglobulin therapy within 1 month (self-report,
onsite enquiry);

- Known or suspected severe illness includes: respiratory illness, acute infection or
active attacks of chronic illness, liver and kidney disease, severe diabetes
mellitus, malignant tumor, infectious or allergic skin disease, Human
Immunodeficiency Virus (HIV) infection (self-report, onsite enquiry, provide test
report if available);

- With hospital-diagnosed serious cardiovascular diseases (cardiopulmonary failure,
drug-uncontrolled hypertension (physical examination of systolic blood pressure ≥
140 mmHg and/or diastolic blood pressure ≥ 90 mmHg), acute attacks of chronic
respiratory illness (self-report, onsite enquiry);

- Received live attenuated vaccines within 1 month before vaccination (self-report,
onsite enquiry);

- Received inactivated vaccines within 14 days before vaccination (self-report, onsite
enquiry);

- Participating or planning to participate in other interventional vaccine clinical
trials during this study

- Other vaccination-related contraindications considered by investigators.