Protein vaccines contain a small part of the pathogen. In the case of the Covid-19 vaccine, it is the spike protein of the coronavirus. This protein covers the surface of the virus like spikes and is therefore easily recognizable by our immune system.
For the vaccine, the spike protein is produced in cell cultures in the laboratory and then purified. A nanoparticle is then added to the spike proteins. This causes the spike proteins to assemble into nanostructures. To increase efficacy, an adjuvant (immune response enhancer) is also added.
The vaccine is then injected into a person's muscle or under the skin. This activates the immune system and as a result for example antibodies are formed against the spike protein. Furthermore, an immunological memory is created in the form of memory B cells that offer protection against later infection.
All three vaccine types against Covid-19 - protein vaccines, and - use the spike protein to activate the immune system. For the protein vaccines, spike proteins are produced in the laboratory and then administered to a human. In contrast, for mRNA and vector vaccines, it is the construction plan of the spike protein that is administered to a human (in the form of mRNA for mRNA vaccines or in the form of DNA for vector vaccines). The human body cells themselves subsequently produce the spike proteins.