Developing a safe and effective COVID-19 vaccine is a global priority to end this pandemic. In their doseescalation, single-centre, open-label, phase 1 trial Published in The Lancet, Feng-Cai Zhu and colleagues1 Report the safety, tolerability, and immunogenicity Of a recombinant adenovirus type-5 (Ad5) vectored COVID-19 vaccine, which expresses the full length spike Glycoprotein of the Wuhan-Hu-1 strain of severe acute Respiratory syndrome corona virus 2 (SARS-CoV-2). Domain because of better immunogenic and protective Potential, but using different antigen delivery platforms (eg, recombinant protein or replicating or non-replicating viral-vector based vaccines and DNA or mRNA vaccines); Several are entering phase 1 clinical trials, or pending results.4, 5 looking forward, other than immunogenicity, Future trial design to establish efficacy will need to define The target groups (eg, health-care workers, individuals at High risk of severe illness), clinical endpoints (eg, reduction In virologically confirmed clinical illness, hospitalizations, Deaths), optimal duration of observation (eg, virus Exposure, side-effects, antibody titre change), and to Anticipate antigenic change over time. Results of this study indicate that some host Factors might affect vaccine response. Suboptimal immunogenicity was reported among older participants, echoing the challenge seen with influenza vaccination. Further study in the older age group and the inclusion of individuals with underlying conditions are important, as they are at risk of severe disease and might benefit most from vaccine prevention.