Rather than depositing bits of viral material directly, the mRNA vaccines instruct your own cells to manufacture a viral antigen (the spike protein), one which is now well understood by itself to play a key role in COVID pathology, despite all the initial insistence that it was harmless. This is absolutely a novel style of delivery. Even Dr. Paul Offit, who sat on the committees which voted to give the mRNA shots their emergency use authorizations, has acknowledged that they may in some cases be stimulating an immune response against the body's own healthy cells and tissues.

hundreds of millions of people vaccinated, an unknowable but definitely large number of lives saved - millions of long covid cases prevented - a handful of people with ongoing health problems from the vaccine. Yup, that tradeoff was worth it and yup i would still describe the mrna vaccine as “harmless”.