Practice question

AZD1222 vaccine known in India as Covishield produced by Serum Institute Pune under license from AstraZeneca Oxford University uses chimpanzee adenovirus vector ChAdOx1. ChAdOx1 derived from chimpanzee adenovirus isolate Y25 taken from chimp stool 1960s, selected because human population seroprevalence low compared to human adenovirus 5 where 40-60 percent adults have neutralizing antibodies compromising vector. Vector engineered by deleting E1 genes essential for replication making it replication deficient incapable of causing disease, requiring E1 complementing cells HEK293 for manufacturing, and deleting E3 region enhancing immunogenicity and cloning capacity. SARS-CoV-2 spike gene codon optimized full length with leader sequence tPA inserted under CMV immediate early promoter in E1 locus. After injection vector enters cells via CAR receptor, traffics to nucleus, does not integrate, transcribes spike mRNA, translates spike glycoprotein expressed on cell surface in prefusion conformation triggering anti spike IgG neutralizing RBD binding ACE2, Th1 biased CD4 response and cytotoxic CD8. Clinical trials showed 70-90 percent efficacy against severe disease, easy storage at 2-8C suiting low income countries, distinguishing from human adenovirus 5 vector Sputnik. Thus chimpanzee adenovirus chosen to avoid anti-vector immunity.