A messenger RNA vaccine (mRNA) refers to a vaccine that uses a person’s own cells to create the antigen that catch the immune system’s attention and initiate the immune response to develop immunity against a pathogen. Messenger RNA tells cells how to make a particular protein, much like a recipe shows how to make a certain food dish. In the case of a vaccine, the protein that gets made will be some part of the pathogen, such as the spike protein on a coronavirus, that the immune system will recognize as an intruder.
An mRNA vaccine contains these instructions on tiny pieces of mRNA that, once injected into a person, enter some of its cells. There, the cells “read” the mRNA “recipe” and begin making the protein. Then the cells release that protein, which immune system cells will see and then signal the alarm that there’s an intruder the immune system must protect against. In a vaccine that has been adequately tested for safety, the protein that the body’s cells make — the imitation of what would be on the pathogen, like a virus’s spike protein — will not cause any harm. In addition, the mRNA itself will eventually self-destruct, at which point the cells will stop making that protein and will then carry on with their other usual cell activity. An mRNA vaccine is designed to stimulate the body to make just enough of a particular antigen that it will prompt the immune system to create antibodies and other related immune responses that will enable it to fight off the real pathogen if it’s encountered.