A traditional vaccine delivers the thing your immune system should learn to recognise: a weakened virus, or a purified piece of one. An mRNA vaccine delivers the recipe instead.
What is in the vial
Two components matter. The first is a strand of messenger RNA encoding one viral protein — for SARS-CoV-2, the spike. The second is a lipid nanoparticle, a tiny bubble of fat that protects the fragile RNA and helps it cross a cell membrane.
Once inside, the mRNA reaches the ribosomes, the cell's protein factories. They read it exactly as they read the cell's own messenger RNA and produce copies of the viral protein. Those copies are displayed on the cell surface, the immune system notices a shape it does not recognise, and it builds antibodies and memory cells against it.
Why it does not change your DNA
Messenger RNA never enters the nucleus, where DNA is kept. Human cells also lack reverse transcriptase, the enzyme that would be needed to write RNA back into DNA. The message is read a limited number of times and then broken down by ordinary cellular machinery, typically within a few days.
Why it took decades to arrive
Injected RNA used to trigger a violent inflammatory response and degrade almost immediately. The fix, developed by Katalin Karikó and Drew Weissman and recognised with the 2023 Nobel Prize in Physiology or Medicine, was to swap one of the RNA building blocks for a modified version. The altered strand slips past the immune sensors that would otherwise destroy it on arrival.
The lipid nanoparticle solved the second half of the problem: getting the message into a cell at all.
