PROS1 and infection: These candidate vaccines are designed to target the four structural proteins composing the SARS-CoV-2 virion: (i) the spike (S) protein, which mediates binding, entry, and attachment to host cells, (ii) the membrane (M) protein, a component of the envelope of the virion, (iii) the envelope (E) protein, which is required for infection, and (iv) the nucleocapsid (N) protein, which forms the ribonucleoprotein core [84].