Global phase III trial of Recombinant Novel Coronavirus Vaccine (Adenovirus Type 5 Vector) (Ad5-nCoV) in adults 18 years of age and older

INTERVENTION: Cohort 1:0.5ml, once by Intramuscular;Cohort 2:0.5ml, once by Intramuscular;Cohort 3:0.5ml, once by Intramuscular;Cohort 4:0.5ml, once by Intramuscular; CONDITION: Novel Coronavirus Pneumonia (COVID‐19) PRIMARY OUTCOME: The efficacy of Ad5‐nCoV in preventing virologically confirmed (PCR positive) COVID‐19 disease occurring 28 days to 52 weeks after vaccination, regardless of severity;To evaluate the incidence of serious adverse events (SAE) and medically attended adverse events (MAE) within 52 weeks after vaccination in all participants; SECONDARY OUTCOME: To evaluate the efficacy of Ad5‐nCoV in preventing virologically confirmed (PCR positive) COVID‐19 disease occurring 14 days to 52 weeks after vaccination, regardless of severity;To evaluate the efficacy of Ad5‐nCoV in preventing severe COVID‐19 disease caused by SARS‐CoV‐2 infection from 14 and 28 days, to 24 and 52 weeks after vaccination;Evaluate the incidence of solicited adverse reactions within 7 days after vaccination ;Evaluate the incidence of unsolicited adverse events within 28 days after vaccination ;Evaluate the seroconversion rate of S‐RBD IgG antibody on Day 28, Week 24 and Week 52 after vaccination, measured by ELISA ;Evaluate the GMT of S‐RBD IgG antibody on Day 28, Week 24 and Week 52 after vaccination, measured by ELISA ;Evaluate the GMI of S‐RBD IgG antibody on Day 28, Week 24 and Week 52 after vaccination, measured by ELISA;Evaluate the seroconversion rate of pseudo‐virus neutralizing antibody on Day 28, Week 24 and Week 52 after vaccination;Evaluate the GMT of pseudo‐virus neutralizing antibody on Day 28, Week 24 and Week 52 after vaccination;Evaluate the GMI of pseudo‐virus neutralizing antibody on Day 28, Week 24 and Week 52 after vaccination;Evaluate the positive rate and level of IFN‐? stimulated by peptide pool of S protein on Day 28, and Weeks 24 and Week 52 after vaccination, measured by ELISpot;Evaluate the positive rate and level of IL‐2, IL‐4, IL‐13, IFN‐? stimulated by peptide pool of S protein on Day 28, and Weeks 24 and Week 52 after vaccination; INCLUSION CRITERIA: 1. Adults of 18 years of age, and older; 2. Able and willing (in the Investigators opinion) to comply with all study requirements; 3. Willing to allow the investigators to discuss the volunteers medical history with their General; 4. Practitioner/personal doctor and access all medical records when relevant to study procedures; 5. Healthy adults, or stable‐healthy adults who may have a pre‐existing medical condition that does not meet any exclusion criteria. A stable medical condition is defined as disease not requiring significant change in therapy or hospitalization for worsening disease during the 3 months before enrollment [4]; 6. For females of childbearing potential only, willingness to practice continuous effective contraception (see glossary) for 30 days prior to enrollment in the study, for 90 days after receiving vaccination during the study, and have a negative pregnancy test on the day(s) of screening/ vaccination (Day 0); 7. Males