This study checks how safe and effective a new flu vaccine is for people aged 50 and older. The vaccine uses mRNA, a kind of genetic code that helps the body make proteins to fight the flu. Participants will get one injection of either a new hexavalent (six-part) vaccine, a trivalent (three-part) vaccine, or a usual flu vaccine. The study lasts about 12 months.

• Participants need to visit the study site for five check-ups and have one phone call check-up.
• Participants will receive compensation for their time and travel.
• Possible mild side effects include soreness at the injection site or mild flu-like symptoms.

To join, you must be 50 or older, not pregnant, and willing to use birth control if needed. You cannot join if you have certain health issues like a weak immune system or a history of severe allergic reactions. Also, if you've recently received certain vaccines or are part of another study, you cannot participate. If you have any questions or need more details, contact the study team.