Immuno-bridging Study of Inactivated SARS-CoV-2 Vaccine in Healthy Population Aged 3-17 vs Aged 18 Years Old and Above

Inclusion Criteria: * Healthy subjects aged 3 years old and above * Medical history and physical examination of the subject confirms the subject is in a healthy condition and is approved by the investigator * Female subjects of childbearing age who are not nursing or pregnant at the time of enrolment (negative urine pregnancy test) and have no family planning within the first 3 months after enrolment. Effective contraceptive measures have been taken within 2 weeks before inclusion. * The subject must be able and willing to complete the whole immunization schedule of the study and be able to follow up study procedures for 6 months. * With self-ability to understand the study procedures, the informed consent \& voluntarily sign an informed consent/ assent form. Legal authority or parents/guardians of minors 3-17 years should sign an informed consent form and be able to comply with the requirements of the clinical study protocol. Exclusion Criteria: * Confirmed acute cases of SARS-CoV-2 infection. * With a medical history of SARS, MERS virus infection (self-report, on-site inquiry); * Fever (axillary temperature \> 37.0 ℃), dry cough, fatigue, nasal obstruction, runny nose, pharyngeal pain, myalgia, diarrhea, shortness of breath and dyspnea within 14 days before vaccination (Tympanic temperature / Temporal artery temperature \>37.5 ℃); * Positive urine pregnancy test result. * Body temperature axillary ≥ 37.0 ℃ before vaccination（Tympanic temperature / Temporal artery temperature≥ 37.5 ℃); * With previous severe allergic reactions (such as acute allergic reactions, urticaria, skin eczema, dyspnea, angioneurotic edema or abdominal pain) or allergy to known ingredients of the inactivated SARS-CoV-2 vaccine. * With a medical history or a family history of convulsion, epilepsy, encephalopathy or mental illness. * With congenital malformation or developmental disorder, genetic defects, severe malnutrition, etc.; * With known or suspected diseases include acute respiratory diseases (e.g. influenza like illness, acute cough, sore throat), severe cardiovascular diseases, severe liver diseases, severe kidney diseases, uncontrollable hypertension (systolic blood pressure \> 150 mmHg, diastolic blood pressure \> 90 mmHg), diabetic complications, malignant tumors, various acute diseases, or acute attack period of chronic diseases. * Has been diagnosed with congenital or acquired immune deficiency, HIV infection, lymphoma, leukemia or other autoimmune diseases; With a history of coagulation dysfunction (such as coagulation factor deficiency, coagulation disease); * With a history of coagulation dysfunction (such as coagulation factor deficiency coagulation disease); * Receiving anti-TB therapy. * Receiving immune enhancement or inhibitor therapy within 3 months (continuous oral or IV administration for more than 14 days); * Vaccinated live attenuated vaccine within 1 month before vaccination and other vaccines within 14 days before vaccination; * Received blood products within 3 months before vaccination; * Received other investigational drugs within 6 months before vaccination; * Other circumstances judged by investigators that were not suitable for participating in this clinical trial.