Covid-19 vaccine, conceptual illustration. The modified adenovirus particles (blue) are carrying a DNA (deoxyribonucleic acid, white helix) sequence for the SARS-CoV-2 spike protein. The SARS-CoV-2 virus (spheres) is the cause of the respiratory disease Covid-19. When injected into the body, the adenovirus infects the body's cells, which start to make copies of the spike protein. The protein stimulates an immune response, causing the body to produce antibodies against it. This means that the body is primed to attack the virus should it be encountered after vaccination, preventing disease.