RNA vaccines such as Pfizer and Moderna’s vaccines against SARS-COV-2 are formulated in lipid nanoparticles and are injected intramuscularly. Muscle cells produce the vaccine antigen protein from the RNAs initiating immune responses to vaccination. This image shows two muscle fibers (cells) shining with a fluorescent protein produced from RNAs at 5 days post intramuscular administration of RNA-loaded lipid nanoparticles. The RNA platform used here is an emerging class of RNAs called self-replicating RNA that copies itself inside the cells following injection and thereby allows for sustained vaccine exposure for up to a month from a small initial dose (In traditional RNA vaccines, antigen expression last for only a few days).

Blue color shows the nuclei, and red and green colors show the fluorescent protein (red color is the fluorescence of the protein itself and green is the fluorescence of a detection protein recognizing the fluorescent protein).