What is this promising COVID-19 vaccine developed by Moderna?

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This article was originally published on Point-Science

In mid-May, the American company Moderna announced that the vaccine developed against COVID-19 had triggered1 an immune response in 8 patients. These patients secreted antibodies in an amount comparable to those seen in infected patients and recovered from the coronavirus. Among the panoply of vaccine strategies currently being tested, to which category does Moderna belong?

The company has bet on an mRNA vaccine2, an intermediate molecule that comes from DNA and that serves as a matrix for protein synthesis. In this genetic strategy, the RNA coding for a specific protein of SARS-CoV-2 is injected: protein S (for “Spike”) which serves as an entry point for the virus into cells. The body will then produce this viral protein itself, triggering an immune system reaction which will then make antibodies against this protein.

For this type of vaccine, the mRNA must be delivered3 directly into the cytoplasm of the cell (medium encountered inside the cells). Moderna therefore encapsulated the mRNA in small assemblies of lipids, which merge with the endosomes* and thus cross the cell membrane.

The main advantages4 of this strategy are that it can be developed quickly and at low cost because it is based on chemical synthesis, requiring no cell culture, fermentation or animals. However, this strategy has never been authorized in humans and the encouraging results observed are only the first step in this clinical trial.

Find out more about the different stages of vaccine production5.

* cellular sub-compartment which can accumulate molecules and release their content in different places of the cell.