Adenovirus vector vaccine, illustration. The modified adenovirus particles (blue) are carrying DNA (deoxyribonucleic acid, white helix) from a pathogenic virus (spheres). When injected into the body, the adenovirus infects the body's cells (brown), which start to make copies of the proteins encoded in the viral DNA. The proteins stimulate an immune response, causing the body to produce antibodies against them. This means that the body is primed to attack the virus should it be encountered after vaccination, preventing disease.