A Phase IIb Clinical Trial to Evaluate the Efficacy, Safety and Immunogenicity of Two Doses of Recombinant Novel Coronavirus Vaccine (Adenovirus Type 5 Vector) in Adults 18 Years of Age and Older, Living With HIV.

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Primary Safety Objectives: * 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 HIV viral load 24 and 52 weeks after vaccination * Evaluate the incidence of serious adverse events (SAE) and medically attended adverse events (MAE) within 52 weeks after vaccination in all participants. Primary Immunogenicity Objectives: * Evaluate the seroconversion rate of S-RBD IgG antibody on Day 28, Day 84 and Week 24 and Week 52 after vaccination, measured by ELISA. * Evaluate the immunogenicity of two doses of the vaccine. Secondary Safety Objectives: * Evaluate the incidence of a decrease in CD4+ cell count by ≥20% at 24 and 52 weeks after vaccination. * Evaluate changes in the CD4/CD8 ratio at 24 and 52 weeks compared to the basal value. * To evaluate the efficacy of two doses of Ad5-nCoV in different age groups from 14 and 28 days to 24 and 52 weeks after vaccination. This will be evaluated by weekly participant contact to assess for any signs or symptoms of COVID 19. Secondary Immunogenicity Objectives: * Evaluate the GMT of S-RBD IgG antibody on Day 28, Day 84 and Week 24 and Week 52 after vaccination, measured by ELISA. * Evaluate the GMI of S-RBD IgG antibody on Day 28, Day 84 and Week 24 and Week 52 after vaccination, measured by ELISA. * Evaluate the seroconversion rate of pseudo-virus neutralizing antibody on Day 28, Day 84 and Week 24 and Week 52 after vaccination. * Evaluate the GMT of pseudo-virus neutralizing antibody on Day 28, Day 84 and Week 24 and Week 52 after vaccination. * Evaluate the GMI of pseudo-virus neutralizing antibody on Day 28, Day 84 and Week 24 and Week 52 after vaccination. * Evaluate the positive rate and level of IFN-γ, TNF, IL-4, IL-5, IL-13 stimulated by peptide pool of S protein on Day 28, Day 84 and Weeks 24 and Week 52 after vaccination, measured by intracellular cytokine staining (ICS) (in a subset of approximately 50 participants). Exploratory Objectives * To evaluate the efficacy of two doses of Ad5-nCoV in preventing virologically confirmed (PCR positive) COVID-19 disease occurring 14 days and 28 days to 52 weeks after vaccination, regardless of severity. * To evaluate the efficacy of two doses of Ad5-nCoV in preventing virologically (PCR) or serologically (four-fold increase in SARS-CoV-2 anti-N IgG from pre-immunization to post symptom, defined as Day 21-28 post illness blood test, or pre-symptom to post-symptom blood test) confirmed COVID-19 disease occurring 14 and 28 days to 52 weeks after vaccination, regardless of severity. * To evaluate the efficacy of two doses 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. Severe disease is defined as: 1) Clinical signs at rest indicative of severe systemic illness (respiratory rate ≥ 30 per minute, heart rate ≥ 125 per minute, SpO2 ≤ 93% on room air at sea level or PaO2/FiO2 \< 300 mm Hg), 2) Respiratory failure (defined as needing high-flow oxygen, non-invasive ventilation, mechanical ventilation or ECMO), 3) Evidence of shock (SBP \< 90 mm Hg, DBP \< 60 mm Hg, or requiring vasopressors), 4) Significant acute renal, hepatic, or neurologic dysfunction, 5) Admission to an ICU * Evaluate the efficacy of Ad5-nCoV in preventing asymptomatic disease of COVID-19 (confirmed by N IgG antibody on week 52 after vaccination). * Evaluate the severity of COVID-19 cases among vaccine recipients (based on WHO or FDA criteria) as compared to the control group, to measure antibody-mediated disease enhancement (ADE). * Evaluate for any evidence of SARS-CoV-2 virus shedding in COVID-19 cases that occurred 28 days to 52 weeks after vaccination (detection of viral nucleic acid every 2 days after being confirmed). * Perform genotyping of SARS-CoV-2 virus isolates of COVID-19 cases that occurred 28 days to 52 weeks after vaccination. * Evaluate incidence of suspected but unconfirmed cases of COVID-19 (either because of negative or no tests).