This study is about the human body's response to the Yellow Fever Vaccine, which uses a weak form of the virus to safely mimic an infection. Yellow fever is a serious disease spread by mosquitoes that can cause liver and kidney problems. About 200,000 people get it every year in South America and Africa. The vaccine is recommended for people 9 months and older going to these areas. Participants will get the vaccine and be part of the study for 1 month to 1 year, based on their immune response. The study aims to learn more about how the vaccine works and improve its safety.

• Study lasts from 1 month up to a year.
• Participants must not take other live vaccines 30 days before or after the study vaccine.
• Women must use birth control and take a pregnancy test before joining the study.

To join, you should be between 18-45 years old, healthy, and able to give consent. You can't join if you have had the yellow fever vaccine before or have certain health conditions like immune system problems, allergies to vaccine components, or if you are pregnant or breastfeeding.