BNT162b2 is an mRNA vaccine. This means that it contains pieces of genetic material that serve as a template for the actual vaccination: the mRNA is channeled into the human cells as a messenger of information. It is encoded on the composition of the protein that triggers the actual vaccination reaction. This vaccination involves parts of the so-called spike protein, also called sting protein in German. This is the part of the virus that the immune system recognizes as hostile, only to unleash a whole body of immune cells that eliminate the pathogen. The cells produce this protein themselves from the template. The mRNA is then either broken down or disintegrates by itself.
Unlike vaccines, with which, for example, protein parts are administered directly, BNT162b2 does not require an active enhancer (adjuvant). Once the mRNA has made it into the cells, it can develop its effect without any auxiliary means. The research team that developed the vaccine, however, had to find a way to safely smuggle the mRNA into the cells: They provided the mRNA with a coat of lipid nanoparticles. These are spherical molecules that are made up of fatty acids and shield their cargo in a cavity from the environment. If the researchers were to leave out this taxi, the mRNA would be destroyed before it reached the inside of the cells.
The active ingredient is injected directly into the muscle using a syringe. In order to optimally prepare the immune system for a real infection, two doses of vaccine are required for BNT162b2. The first is called the prime dose because it is supposed to stimulate the immune system, but above all it is there to pave the way for the second booster dose. According to the manufacturer, both doses should provoke a stronger immune reaction than one alone.