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.
The goal of this clinical trial is to assess the immune response to the yellow fever vaccine 17D in adults with prior 17D vaccination. The main questions this study aims to answer are:~how does prior vaccination affect antibody responses to re-vaccination?~how does prior vaccination affect the immune cell response to re-vaccination?~Participants will:~have been previously vaccinated with 17D.~be re-vaccinated with 17D.~provide medical and travel histories.~provide a blood sample prior to vaccination~provide a blood sample approximately every other day for 14 days after vaccination.~provide a blood sample approximately 28 days after vaccination.~complete a daily diary of symptoms following vaccination for 14 days.~report any additional symptoms after 14 days.