The past few months have brought a number of scientific terms to public attention. We’ve had to digest R (a virus’s reproduction number) and PCR (the polymerase chain reaction method of testing). And now there’s mRNA. This last one has featured heavily in recent news reports because of the spectacular results of two new mRNA vaccines against coronavirus. It stands for “messenger ribonucleic acid”, a label familiar enough if you studied biology at O-level or GCSE, but otherwise hardly a household name. Even in the field of vaccine research, if you had said as recently as 10 years ago that you could protect people from infections by injecting them with mRNA, you would have provoked some puzzled looks.
Essentially, mRNA is a molecule used by living cells to turn the gene sequences in DNA into the proteins that are the building blocks of all their fundamental structures. A segment of DNA gets copied (“transcribed”) into a piece of mRNA, which in turn gets “read” by the cell’s tools for synthesising proteins. In the case of an mRNA vaccine, the virus’s mRNA is injected into the muscle, and our own cells then read it and synthesise the viral protein. The immune system reacts to these proteins – which can’t by themselves cause disease – just as if they’d been carried in on the whole virus. This generates a protective response that, we hope, lasts for some time. It’s so beautifully simple it almost seems like science fiction. But last week we learned that it was true.
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Adam Finn is professor of paediatrics at the Bristol Children’s Vaccine Centre, University of Bristol
