The study is about learning how the human body fights the flu after receiving the flu vaccine. The flu, also known as influenza, is a virus that changes a lot, making it tough to develop vaccines that work well. The live attenuated influenza vaccine (LAIV) is a special type of vaccine given as a nasal spray. It works well in kids but not as well in adults. This study wants to figure out why. If you are between 18-49 years old and haven't had a flu vaccine recently, you might be able to join the study. You'll receive the nasal spray vaccine and be asked to visit the research center 3 times over one month. The team will take samples from your blood and nose to see how your immune system reacts.

• Three visits over 1 month are needed.
• Participants receive a nasal spray vaccine.
• Samples collected from blood and nose.

Remember, not everyone can join. If you have certain medical conditions or have had the flu vaccine recently, you might not be eligible. Participation is voluntary, and you should talk to the research team if you have questions.