Immunogenicity of Yellow Fever Vaccine 17D in Adults With Prior 17D Vaccination

In this study the investigators use 17D revaccination as a live-virus challenge to test the hypothesis that neutralizing antibody titers correlate with YFV protection. The investigators will prospectively characterize pre-boost antibodies titers, vaccine viremia, acute immune responses and post-boost titers in vaccinees receiving boost 17D vaccinations. The investigators expect to identify neutralizing antibody titers above which sterilizing immunity is conferred and titers below which it is not. These Aims will set a foundation for future studies to further dissect determinants of 17D and other live-attenuated vaccine induced immunity and establish metrics that could allow efficient prioritization of 17D vaccination and optimize 17D use in the face of current and future outbreaks.