ZyCOV-D is a "plasmid DNA" vaccine. That is, it uses a genetically engineered , non-replicating version of a type of DNA molecule called a "plasmid". Here, the plasmids are coded with the instructions to make the spike protein of SARS-CoV-2 (the Coronavirus causing COVID-19) Vaccination gives the code to cells in the recipient’s body. Then they can begin to make the spiky outer layer of the virus. The immune system is expected to recognise it as a threat and develop antibodies by way of response.