The medicine can be a recipe the cell cooks

An mRNA vaccine delivers a temporary recipe, inside a droplet of fat, and the cell makes the protein. The recipe is not written into the genome.

Messenger RNA is what a cell uses, anyway, to carry a gene’s text from the nucleus to the ribosomes that build proteins. The laboratory version is modified so the cell’s innate immune sensors do not shred it on sight — the work that won Katalin Karikó and Drew Weissman their prize — and it is wrapped in a lipid nanoparticle so it can cross a membrane. Once inside, ribosomes build the protein the RNA names. The RNA has no machinery for entering the nucleus and no reverse transcriptase riding with it. It is translated, and it is broken down, on a timescale of days.

The hard engineering was the wrapper and the modified letters, not the idea of a recipe. Naked RNA is destroyed almost immediately in the body. The droplet of fat is the delivery van, and designing it so that it dumps the cargo in the right place, without being itself a toxin, took decades. The 2020 vaccines are the public proof that the van can arrive.