The AstraZeneca COVID-19 vaccine works by using a harmless chimpanzee adenovirus as a vector to deliver genetic instructions (DNA) into human cells. These instructions code for the SARS-CoV-2 spike protein. The adenovirus vector enters human cells, and its DNA is transported to the cell nucleus. There, the cell uses the DNA to produce messenger RNA (mRNA), which then directs the production of the spike protein by the cell. These spike proteins, displayed on the cell surface, trigger the immune system to produce antibodies and activate T cells. This immune response prepares the body to recognize and fight the real coronavirus if exposed later. The adenovirus used is replication-deficient, meaning it cannot replicate inside human cells or cause disease. The vaccine requires two doses, usually given 4 to 12 weeks apart, to build effective immunity.
