Vaccines have worked in the same way since they were invented more than 200 years ago: they use a weakened version of the targeted virus to create an immune response that the body remembers. Since COVID-19 appeared, a new kind of vaccine has emerged -- the mRNA vaccine. The mRNA vaccine is a unique delivery system that focuses specifically on the cells that are the targets of an infection. And, as UH infectious disease specialist Robert Salata, MD, explains, researchers are now studying how to use this revolutionary technology to fight other diseases such as HIV, rabies and influenza.