The U.S. Food and Drug Administration has approved Moderna's mRNA-based seasonal flu vaccine, marking the first time an mRNA flu shot has been cleared for use. The approval comes after the FDA initially declined to review the vaccine, though the agency later reversed course and gave it the green light. The vaccine uses the same messenger RNA technology that proved successful in Moderna's COVID-19 shots. The approval is seen as a significant step in expanding mRNA technology to other diseases. The vaccine is designed to protect against seasonal influenza, which causes hundreds of thousands of hospitalizations annually in the United States. Moderna had submitted the vaccine for approval, but the FDA had originally refused to review it. The agency did not give a reason for the initial refusal or the subsequent approval. The announcement was made this week, and the vaccine is expected to become available for the upcoming flu season. The approval also adds to a growing list of mRNA-based treatments and vaccines being developed for various conditions.