In this study, an experimental medicine investigation that leverages on a recently completed clinical trial that the PI led examining how cross-reactive antibodies altered the immunogenicity of yellow fever (YF) vaccination. We will seek to clarify the effects of statin on LAV immunogenicity. YF vaccine is an excellent LAV, which remains the WHO recommended response to the ever-present threat of YF outbreak. It has also served as an important model for studying human antiviral immunity. We propose to test the hypothesis that long term statins therapy alters YF LAV immunogenicity by coupling the power of a clinical trial with comprehensive systems vaccinology to define the impact statins have on the adaptive immune response to YF vaccination. This study will elucidate how statins modulate the networks that drive immunity to vaccination in a fast growing population globally. Knowledge on how statins impact LAV immunogenicity would inform public health authorities on the size of the general population that should be vaccinated to compensate for alterations in immunogenicity in this subpopulation to achieve sufficient herd immunity for epidemic and pandemic control.