Phials of the Oxford-AstraZeneca (left), Pfizer-BioNTech BNT162b2 (marketed as Comirnaty, centre) and Moderna (right) vaccines against SARS-CoV-2, the cause of Covid-19. The Pfizer-BioNTech and Moderna vaccines consists of strands of mRNA (messenger ribonucleic acid) that code for the SARS-CoV-2 spike protein, encased in lipid nanoparticles. The Oxford-AstraZeneca vaccine contains an adenovirus that normally infects chimpanzees that has been altered to contain a DNA (deoxyribonucleic acid) sequence for the SARS-CoV-2 spike protein. All three vaccines when injected and taken up by the body's cells, instruct them to make copies of the spike protein, which stimulates an immune response, causing the body to produce antibodies against the spike protein. This means that the body is primed to attack the virus should it be encountered after vaccination, preventing disease.