The Pfizer/BioNTech vaccine is a lipid nanoparticle-formulated mRNA vaccine. The mRNA encodes the SARS-CoV-2 full length spike protein. The mRNA in the vaccine is translated and transcribed by the body to produce the spike protein. The protein then acts as an intracellular antigen to stimulate the immune response. The mRNA in the vaccine is normally degraded within a few days and cannot incorporate into the host genome. Data from the Pfizer/BioNTech vaccine trials undertaken in over 40,000 individuals indicate high vaccine efficacy, with no serious safety concerns observed.
AstraZeneca COVID-19 vaccine
AstraZeneca COVID-19 vaccine uses a replication deficient chimpanzee adenovirus as a vector that encodes the full-length SARS-CoV2 spike protein. Chimpanzee adenoviruses are non-enveloped viruses, meaning that the glycoprotein antigen is not present on the surface of the vector, but is only expressed at high levels once the vector enters the target cells. Genes are inserted to render the virus replication incompetent, and to enhance immunogenicity. Once the vector is in the nucleus, mRNA encoding the spike protein is produced that then enters the cytoplasm. This leads to translation of the target protein which acts as an intracellular antigen. Headline data from vaccine trials undertaken indicate high vaccine efficacy, with no serious safety events related to the vaccine.