The U.S. Food and Drug Administration (FDA) has approved a new seasonal flu vaccine that uses mRNA as its base. Similar to mRNA vaccines against COVID-19, the vaccine uses the genetic molecule mRNA to encode instructions for cells in the body. Flu viruses use this protein to infiltrate human cells, and it's the same protein targeted by conventional flu vaccines. Half received the mRNA-based shot, and half received a standard dose of a conventional flu vaccine (as opposed to the higher-dose option available to older adults in the U.S.). That means the mRNA vaccine was 26.6% more protective than the conventional vaccine against illness from flu in this trial.