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This system eventually stops the first attack of a virus and allows your body to do a better job the next time it sees that virus. . But for viruses that make you sick--like COVID or influenza--it's better to prime your immune system so it can attack the virus the first time it shows up. That's what vaccines do. Conventional vaccines operate by injecting a weakened or dead form of the virus you're trying to stop. Your immune system sees the new shapes on the virus, kicks into gear, and builds up immunity. With a weakened virus, there is always the question of whether it was weakened enough--if it wasn't, it might mutate back into a form that can cause disease. But if it was weakened too much, it won't activate a strong immune response in your body. Likewise, killed viruses often don't trigger much of an immune response. The idea behind mRNA vaccines was ingenious. Since mRNA takes the orders for proteins from the DNA and delivers them to the cooks in your cells' kitchen, what if we could change those orders in a very targeted way? By teaching your cells to make shapes that match shapes on the actual virus, the vaccine would trigger your immune system without having to introduce the virus itself. If they could be made, mRNA vaccines would be a huge advance over conventional vaccines. Once you had mapped out all the proteins that make up the virus you wanted to target, you'd identify the one that you want antibodies to grab. Then you'd study the virus's genetic code to find the instructions for making that protein, and you'd put that code into the vaccine using mRNA. If, later, you wanted to attack a different protein, you'd just change the mRNA. This design process would take at most a few weeks. You would ask the waiter for fries instead of a side salad, and your immune system would do the rest.