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 of CNBG inactivated COVID-19 vaccine according to the
product insert;

- Female subjects who are not nursing or pregnant at the time of enrolment (negative
urine pregnancy test) and have no family planning within the first 6 months after
enrolment. 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; Self has 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 SARS and MERS infection (self-report, on-site inquiry);

- Has vaccinated with any vaccine other than one or more doses of CNBG inactivated
COVID-19 vaccine;

- Axillary temperature ≥ 37.3 ℃ (forehead temperature ≥ 37.8 ℃);

- Previous severe allergic reactions to vaccination (such as acute allergic reactions,
urticaria, dyspnea, angioneurotic edema or abdominal pain) or allergy to known
components of recombinant COVID-19 vaccine;

- Allergic to any component of the study vaccine (e.g. aluminum, histidine, etc.)

- Known or suspected diseases include：Severe respiratory diseases, severe liver and
kidney diseases, hypertension (systolic blood pressure ≥ 150 mmHg, diastolic blood
pressure ≥ 90 mmHg), diabetic complications, malignant tumors, various acute
diseases or acute attacks of chronic diseases;

- Has been diagnosed with congenital or acquired immunodeficiency, HIV infection,
lymphoma, leukemia or other autoimmune diseases;

- Has a history of convulsions, epilepsy, encephalopathy，long term history of alcohol
and drug abuse, history of thyroidectomy, infectious diseasesor mental illness or
family history（lineal）;

- With Congenital malformation or developmental disorder, genetic defect, severe
malnutrition, etc.;

- Has a history of coagulation dysfunction (e.g. coagulation factors deficiency and
coagulation diseases);

- Absence of spleen or splenectomy, functional absence of spleen caused by any
condition

- Anti -TB (TB) treatment is under way.

- Patients receiving immunoenhancement or inhibitor therapy within 3 months
(continuous oral or IV administration for more than 14 days);

- Received other vaccines within 14 days before vaccination；

- Received blood products before within 3 months before vaccination;

- Received other investigational drugs within 6 months before vaccination;

- Plan to move before the end of the study or leave the local area for a long time
during the scheduled study visit

- Other circumstances judged by investigators that are not suitable for this clinical
trial