A Study to Evaluate the Safety and Immunogenicity of Ad5-nCoV and Ad5-nCoV-IH in CoronaVac Immunized Children and Adolescents

Inclusion Criteria: 1. Children aged 6-12 years and adolescents aged 13-17 years at the time of randomization. 2. Have received a complete two dose schedule of CoronaVac for ≥ 90 days. 3. Obtain written informed assent from participants and consent from parents, guardians or legal representatives. 4. Subjects are eligible for immunization of this product as evaluated by investigators after medical history examination, physical examination and clinical judgment of health. Exclusion Criteria: 1. Have a history of seizures, epilepsy, encephalopathy, psychosis. 2. History of anaphylaxis to any vaccine component. 3. Positive urine pregnancy test result, pregnant, lactation women. Female had menarche must conduct the urine pregnancy test. 4. Congenital or acquired angioedema/neuroedema . 5. Medical history of Guillain-Barré syndrome. 6. Have had asthma attacks within 2 years. 7. Have severe nasal or oral diseases, such as rhinitis (sinusitis), allergic rhinitis, oral ulcer, throat swelling, etc. 8. Asplenia or functional absence of spleen. 9. Bleeding disorder (e.g. protein S or factor deficiency, coagulopathy or platelet disorder). 10. Any confirmed or suspected immunosuppressive or immunodeficient state; received immunosuppressive therapy, cytotoxic therapy, or chronic corticosteroids (excluding corticosteroid spray therapy for allergic rhinitis and surface corticosteroid therapy for acute non-complicated dermatitis) within the past 6 months. 11. Have chronic systematic infection or chronic pulmonary disease 12. Administration of immunoglobulins and/or any blood products within three months prior to the planned administration of the vaccine candidate. 13. Receiving anti-tuberculosis or cancer treatment. 14. History of COVID-19 disease. 15. Have a positive result at the examination of rapid SARS-CoV-2 antibody assay (S-RBD IgG) before vaccination. 16. Have received COVID vaccines other than CoronaVac. 17. Received or plan to receive any non-COVID vaccines (licensed or investigational), within 14 days before and after study vaccination. 18. Current diagnosis of or treatment for cancer, e.g. leukemia. 19. Any other significant disease, disorder or finding which may significantly increase the risk to the volunteer because of participation in the study, and affect the ability of the volunteer to participate in the study or impair interpretation of the study data.