Immunogenicity and Safety Study of One Booster Dose of Trivalent COVID-19 Vaccine (Vero Cell), Inactivated

Inclusion Criteria: * Healthy people aged 3 years and above who have completed two or three doses of CoronaVac at least 3 months (≥ 90 days) before (3-8 weeks interval for the first and second dose of CoronaVac, and ≥3 months interval for the second and third dose); * Participants (and/or their legal guardians for pediatric population) are able to understand and sign the informed consent voluntarily; * Pregnancy and contraception: Female participants of childbearing potential (post-menarche and pre-menopause that has not been undergone any sterilization surgery), who have a negative pregnancy test on the day of booster vaccination in the present study, has practiced adequate contraception or has abstained from all activities that could result in pregnancy for at least 28 days prior to the day of vaccination, and agree to continue adequate contraception through 3 months following the booster vaccination and are not currently breastfeeding; Male participants of childbearing potential who agree to use adequate contraception through 3 months following the booster vaccination (and/or your female partner agree to use an acceptable method of birth control), which include refrain from donating sperm; Note 1 :Adequate contraception is defined as consistent and correct use of an approved contraceptive method in accordance with the product label. For example: * Barrier method (such as condoms, diaphragm, or cervical cap) used in conjunction with spermicide * Intrauterine device * Prescription hormonal contraceptive taken or administered via oral (pill), transdermal (patch), subdermal, or IM route * Sterilization of a female participant's monogamous male partner prior to entry into the study Note 2 : Periodic abstinence (eg, calendar, ovulation, symptothermal, post-ovulation methods) and withdrawal are not acceptable methods of contraception. * Participants are able to comply with study procedures based on the assessment of the Investigator; * Participants willing to provide verifiable identification (following the local regulations), to be contacted, and to contact the investigator during the study period. Exclusion Criteria: * History of confirmed infection of SARS-CoV-2 within 3 months prior to study vaccination； * With positive test result of SARS-CoV-2 antigen during screening visit; * Any prior administration of another investigational COVID-19 vaccine or other licensed COVID-19 vaccines, or current/planned simultaneous participation in another interventional study to prevent or treat COVID-19; * Known allergy to vaccines or vaccine ingredients, and serious adverse reactions to vaccines, such as urticaria, dyspnea, angioneurotic edema; * Serious chronic disease, including but not limited to serious cardiovascular disease, hypertension and diabetes that drugs cannot control, hepatorenal disease, malignant tumor, etc; * Acute central nervous system diseases such as encephalitis/myelitis, acute disseminating encephalomyelitis, and related disorders; * Significant chronic central nervous system diseases or neuromuscular disorders, psychosis or severe cognitive behavioral disorder, in the opinion of the investigator, including but not limited to epilepsy, autism spectrum disorder, intellectual disabilities; * History of autoimmune and/or hematological diseases (including but not limited to systemic lupus erythematosus, thyroidectomy, autoimmune thyroid disease, hematological malignancy, asplenia, functional asplenia, or splenectomy resulting from any condition); * History of bleeding disorders (e.g., factor deficiency, coagulopathy or platelet disorder), or prior history of significant bleeding or bruising following IM injections or venipuncture; * Receipt of blood/plasma products or immunoglobulins in the past 3 months before vaccination in this study; * Participation in other studies involving study intervention within 30 days prior to vaccination in this study; * Receipt of attenuated live vaccines in the past 14 days prior to vaccination in this study; * Receipt of inactivated or subunit vaccines in the past 7 days prior to vaccination in this study; * Emerging of chronic diseases or acute exacerbation of stable chronic diseases (including but not limited to asthma, migraine, gastrointestinal disorder, etc.) within 30 days prior to vaccination in this study; * Acute febrile illness, or body temperature ≥37.8°C on the day of vaccination; enrollment could be considered if the fever is absent for 72 hours prior to vaccination; * According to the investigator's judgment, the participant has any other factors that might interfere with the clinical trial results or pose additional risk to the participant due to participation in the study.