1. Ministry of Health, Government of the Republic of Zambia, Lusaka, Zambia;
2. Department of Epidemiology and Biostatistics, University of Georgia, College of Public Health, Athens, Georgia;
3. International Vaccine Access Center, Department of International Health, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland;
4. Department of Epidemiology, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland;
5. Macha Research Trust, Choma, Zambia