1. From the Institute of Child Health, London, United Kingdom (VOO, AMT, SE, TD, and JKW); the University Teaching Hospital, Lusaka, Zambia (LMK); the Lusaka District Health Management Board, Lusaka, Zambia (MMS); the Medical Research Council, Cambridge, United Kingdom (AC); and the London School of Hygiene and Tropical Medicine, London, United Kingdom (SMF)