English: Structure of SARS-CoV-2 and key antigenic components. Illustration of SARS-CoV-2 which is a single stranded RNA virus. The key antigenic components being targeted in vaccine design are shown on the right, consisting of the spike (S), envelope (E), membrane (M), and nucleocapsid (N) proteins. The main emphasis for human vaccines is based on the spike (S) protein, consisting of an S1 binding region and S2 fusion and cell entry region. The S1 domain contains the receptor binding domain (RBD) responsible for binding to the ACE2 receptor on the surface of host cells. Following fusion, the S protein sheds the S1 region and undergoes a dramatic structural change to its post-fusional state in order for the virus to enter the host cells.