In the 20th century, most vaccines took well over a decade to research, test, and produce. But the vaccines for COVID-19 cleared  the threshold for emergency use in less than 11 months. The secret behind this speed  is a medical technology that’s been developing for decades: the mRNA vaccine. This new treatment uses our body’s  existing cellular machinery to trigger an immune response, protecting us from viruses without ever experiencing an infection. And in the future, this approach might be able to treat new diseases almost as quickly as they emerge. So how do these  revolutionary vaccines work? The key ingredient is in the name. mRNA, or messenger ribonucleic acid, is a naturally occurring molecule that encodes the instructions  for producing proteins. When our cells process mRNA,  a part of the cell called the ribosome translates and follows these instructions to build the encoded protein. The mRNA in these vaccines works in exactly the same way, but scientists use the molecule to safely introduce our body to a virus. First, researchers encode trillions  of mRNA molecules with the instructions for a specific viral protein. This part of the virus is harmless by itself, but helpful for training  our body’s immune response. Then, they inject those molecules  into a nanoparticle roughly 1,000 times smaller  than the average cell. This nanoparticle is made of lipids, the same type of fatty material that forms the membrane around our cells. But these lipids have been  specially engineered to protect the mRNA on its journey  through the body and assist its entry into the cell. Lastly, the final ingredients are added: sugars and salt to help keep the nanoparticles intact  until they reach their destination. Before use, the vaccine is kept at a  temperature of -20 to -80 degrees Celsius to ensure none of the components break down. Once injected, the nanoparticles disperse and encounter cells. The lipid coating on each nanoparticle fuses with the lipid membrane of a cell and releases the mRNA to do its work. At this point, we should note  that while the vaccine is delivering viral genetic material into our cells, it’s impossible for this material  to alter our DNA. mRNA is a short-lived molecule that would need additional enzymes and  chemical signals to even access our DNA, let alone change it. And none of these DNA altering components are present in mRNA vaccines. Once inside the cell, the ribosome translates the mRNA’s instructions and begins assembling the viral protein. In COVID-19 vaccines, that protein  is one of the spikes typically found on the virus’s surface. Without the rest of the virus  this lone spike is not infectious, but it does trigger our immune response. Activating the immune system can be taxing on the body, resulting in brief fatigue, fever,  and muscle soreness in some people. But this doesn’t mean  the recipient is sick— it means the vaccine is working. The body is producing antibodies to fight that viral protein, that will then stick around to defend  against future COVID-19 infections. And since this particular protein is likely to be found in most COVID variants, these antibodies should reduce  the threat of catching new strains. This approach offers significant advantages over previous vaccines. Traditional vaccines contain  weakened versions of live viruses or amputated sections of a virus, both of which required time intensive research to prepare and unique chemical treatments to safely inject. But mRNA vaccines don’t actually contain any viral particles, so they don’t have to be built  from scratch to safely adjust each virus. In fact, every mRNA vaccine could have roughly the same list of ingredients. Imagine a reliable, robustly tested vaccine that can treat any disease by swapping out a single component. To treat a new illness, researchers would  identify the right viral protein, encode it into mRNA, and then swap that mRNA  into the existing vaccine platform. This could make it possible to develop new vaccines in weeks, giving humanity a flexible new tool  in the never-ending fight against disease.