to produce an mrna vaccine, scientists produce a synthetic version of the mrna that a virus uses to build its infectious proteins. this mrna is delivered into the human body, whose cells read it as instructions to build that viral protein, and therefore create some of the virus’s molecules themselves. these proteins are solitary, so they do not assemble to form a virus. the immune system then detects these viral proteins and starts to produce a defensive response to them https://horizon-magazine.eu/article/five-things-you-need-know-about-mrna-vaccines.html