How do the Pfizer-BioNTech and Moderna vaccines work?

The Pfizer-BioNTech and Moderna vaccine products use a messenger RNA (mRNA) delivery system. The mRNA is basically a recipe that tells your cells how to make a piece of the virus called the spike protein. Your immune system then uses these pieces of the virus to learn how to recognize it and remove it from the body. While this is new technology for making human vaccines, it has been studied since the 1990’s.