n The pandemic has given rise to scientific acronyms, such as PCR tests, to which we are now familiar. The arrival of vaccines against Covid-19, for its part, has brought about the emergence of mRNA: a new technology based on messenger ribonucleic acid (said mRNA) developed by the firms Pfizer and Moderna. RNA is a bit like DNA’s cousin. In a cell, DNA stays warm in the nucleus. Genetic information leaves the nucleus only in the form of RNA. Pfizer and Moderna produced mRNA in the laboratory, allowing a cell to make a protein characteristic of the Sars-Cov-2 virus. They put her in a bubble of fat and put it all in a syringe. Once injected, mRNA enters cells. They will produce the viral protein in order to train the immune system to recognize it. Unfortunately, mRNA is unstable, it keeps poorly. Vaccines should therefore be stored at -20 ° C for Moderna, and -72 ° C for Pfizer.