1. Medical Research Council Unit The Gambia at the London School of Hygiene and Tropical Medicine , Fajara , The Gambia
2. Regional Health Directorate Upper River Region, Ministry of Health and Social Welfare , Basse , The Gambia
3. Center for Vaccine Development and Global Health, University of Maryland School of Medicine , Baltimore, Maryland , USA
4. Department of Pediatrics, University of Maryland School of Medicine , Baltimore, Maryland , USA