From the Nuffield Department of Population Health, University of Oxford, Oxford, United Kingdom, and the Harvard T.H. Chan School of Public Health, Boston (D.J.H.); the Centre for the Aids Programme of Research in South Africa, Durban, and the Department of Epidemiology, Columbia Mailman School of Public Health, New York (S.A.K.); and the Wellcome Trust, London (J.J.F.).