Inclusion Criteria:  6-59 years of age at the time of enrollment; Able to provide consent or obtain consent from guardian to participate in the trial and sign an Informed Consent Form (ICF); Able and willing to complete all the scheduled study procedures during the whole study follow-up period; Axillary temperature ≤37.0℃; IgG ang IgM negative for Covid-19; Have not received any type of Covid-19 vaccines; No contact history of Covid-19; no travel history to medium and high risk regions and abroad in the past 21 days; Participants who are clinically determined to be healthy after checking medical history and physical examination are eligible to receive the product.  Exclusion Criteria:  Medical or family history of convulsions, epilepsy, encephalopathy, and psychosis disorders; History of allergies to any ingredient of Ad5-nCoV, history of serious allergic reactions to any vaccine, history of allergies and immune diseases; Women who are pregnant or lactating, positive urine pregnancy test or plan to become pregnant during the 12 months study period; Acute febrile diseases and infectious diseases, medical history of SARS (SARS-CoV-1); Serious cardiovascular diseases, such as arrhythmia, conduction block, myocardial infarction, severe hypertension and uncontrollable medications (on-site measurement for 18-59 years of age: systolic blood pressure ≥160mmHg, diastolic blood pressure ≥100mmHg), etc; Severe chronic diseases or with advanced stage conditions which cannot be controlled smoothly, such as diabetes, thyroid disease, etc; Congenital or acquired angioedema/neurological edema; Urticaria history within 1 year before receiving the study vaccine; Asplenia or functional aspleenia; Thrombocytopenia or other coagulation disorders (may cause contraindications for intramuscular injection); Trypanophobia； History of receiving immunosuppressant therapy, anti-allergic therapy, cytotoxic therapy, nebulized corticosteroid therapy in the past 6 months (not including corticosteroid spray treatment for allergic rhinitis, and surface corticosteroid treatment for acute non-complicated dermatitis); Prior administration of blood products in last 4 months; Received other investigational drugs within 1 month before the study; Prior administration of live attenuated vaccines within 1 month before the study; Prior administration of subunit or inactivated vaccines within 14 days before the study; Current anti-tuberculosis therapy; Medical history of Covid-19 disease/infection; Any condition that in the opinion of the investigators may interfere with the participants' compliance or evaluation of study objectives or informed consent (i.e. medical, psychological, social or other conditions, etc.).