The Rationale Behind the Effectiveness of COVID-19 Vaccines and Associated Immunological Mechanisms

The basic concept of vaccination has been based on engendering an adaptive immune response armed with effective immune cells, memory cells, and cytokines. These elements cooperate to mount either a humoral or a cell-mediated response. Coronavirus disease-2019 vaccines, although diversified, adapted the same objective with the previous vaccines prepared since Edward Jenner's work. The spike surface protein (S) and the receptor binding domain constituted the main antigenic determinants for which the binding antibodies as well as the neutralizing antibodies were secreted. The unprecedented use of mRNA vaccines represented an unmatched breakthrough, which paved the road for a new era of vaccine generation. They showed a substantial ability to elicit antibody secretion with a moderate helper T cell response just after inoculation of the first dose. Besides, the adenoviruses-shuttled vaccines were able to engender a spectrum of polyclonal antibodies including neutralizing antibodies apt to drive a multitude of antibodies-mediated functions and activate T cell immune responses. In either case, the antibody titers as well as lymphocytes-mediated responses were significantly intensified. Deciphering the mechanisms of immune response activation by the inoculated vaccines in addition to the elaboration of innate elements involvement should open the door for a better decryption of the induced immune protection and pave the road for the formulation of a more effective vaccine that surmounts the incessant mutational variation of the viral antigenic attributes.