How mRNA vaccines work
Messenger RNA (mRNA) is a short-lived molecule that carries instructions for making a protein. An mRNA vaccine uses this normal cellular process to show the immune system a harmless marker from a pathogen—without exposing the person to the pathogen itself.
Mechanism, step by step
The vaccine delivers instructions.
A laboratory-made strand of mRNA is enclosed in tiny lipid (fat) particles. These particles protect the fragile mRNA and help it enter cells near the injection site.Cells read the mRNA.
Once inside a cell’s cytoplasm, ribosomes—the cell’s protein-making machinery—read the mRNA instructions. The mRNA does not need to enter the nucleus, where DNA is stored.A harmless antigen is produced.
The cell briefly makes a selected protein, or part of a protein, associated with the target pathogen. COVID-19 mRNA vaccines, for example, instruct cells to make the SARS-CoV-2 spike protein. They do not make the whole virus.The immune system detects the antigen.
The protein is displayed to immune cells, which recognize it as foreign. This activates several parts of the immune response, including antibody-producing B cells and T cells that help coordinate or destroy infected cells.Immune memory develops.
Some activated B and T cells become memory cells. If the actual pathogen appears later, these cells can recognize its antigen and respond faster and more strongly, reducing the risk of severe illness.The mRNA is broken down.
Vaccine mRNA is temporary. After cells use the instructions, normal cellular enzymes degrade it. The antigen also disappears over time, while immune memory can persist—although protection may decline, making boosters useful in some cases.
Diagram in words
**Injection → lipid particle carries mRNA into the cell → ribosome reads the instructions → cell makes a harmless viral protein → immune system recognizes it → antibodies and T cells