Study population and methods for analyzing 17DD vaccine–specific neutralizing antibodies and phenotypic/functional cell memory in YF. The primary vaccination arm (reference group) includes participants who have never been vaccinated or have had 1 YF vaccination; secondary vaccination arm includes participants who have received 1 or 2 vaccinations; and multiple doses arm includes participants who have received >2 revaccinations. Participant subgroups indicate number of days or years since vaccination (in parentheses; d0 for those never vaccinated). Participant age ranges are given below subgroup boxes. #PV, had primary vaccination >10 years previously; NV, not vaccinated; PV, had primary vaccination only; RV, revaccinated; YF, yellow fever.