Current vaccine is an actual virus, just a weakened (attenuated) version. mRNA vaccine causes your body to create the proteins that your immune system can targe

Current vaccine is an actual virus, just a weakened (attenuated) version. mRNA vaccine causes your body to create the proteins that your immune system can target if it encounters the actual virus. That allows your immune system to train on the targets without introducing an actual virus. The mRNA version doesn't have the ability to infect a cell and use it to reproduce, it ONLY triggers the immune system.