mRNA vaccine

An mRNA vaccine delivers genetic instructions rather than the antigen itself. It contains messenger RNA that codes for one protein of a pathogen, such as the spike protein of SARS-CoV-2, packed inside lipid nanoparticles, tiny fatty bubbles that protect the fragile RNA and help it enter cells. After an injection into muscle, cells take up the particles and their ribosomes translate the mRNA into the protein. The immune system meets this protein much as it would during an infection and responds with antibodies, helper T cells and killer T cells.

The mRNA never enters the nucleus and cannot change a cell's DNA, and it is broken down within days, so the protein is made only briefly. Early versions set off strong inflammation and produced little protein. Katalin Karikó and Drew Weissman found that swapping uridine for a modified base such as pseudouridine dampened this innate immune alarm and raised protein output, work that won the 2023 Nobel Prize for medicine. Because the RNA is made in a test tube by in vitro transcription, without growing any virus, new vaccines can be designed and produced quickly.

The first two, against COVID-19, were authorized in December 2020, less than a year after the virus was sequenced. Most need cold storage. Researchers are developing mRNA vaccines against influenza, other infections and cancer.