mRNA vaccines contain the construction plan for a specific part of the virus. This construction plans are delivered to our cells in the form of molecules that are artificially produced in a test tube. In the case of the COVID-19 vaccine, the construction plan carries the instructions for producing the spike protein of the coronavirus. This protein covers the surface of the virus like spikes and is therefore easily recognisable by our immune system. In the mRNA vaccine, the mRNA is packed in drops of fat (lipid nanoparticles) to protect it, so that it can enter body cells and is not immediately degraded.
The vaccine is injected into a person's muscle. Once the mRNA has entered or been engulfed by a cell, the cell’s ribosomes read the instructions and produce the spike protein. This protein is then transported to the surface of the cell where it can be detected as an intruder (antigen) by our immune cells. 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.
Both mRNA vaccines and work by delivering to our cells the construction plan to produce the spike protein of the coronavirus. The two vaccine types differ in terms of what they use to deliver these instructions ( in the case of mRNA vaccines and DNA in the case of vector vaccines) and what they use to package their respective genetic material (lipid nanoparticles in the case of mRNA vaccines and a modified adenovirus in the case of vector vaccines).