1. Vaccines and Infectious Disease Analytics (VIDA) Research Unit, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg 2000, South Africa
2. African Social Sciences Unit of Research and Evaluation (ASSURE), Wits Health Consortium, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg 2000, South Africa
3. Perinatal HIV Research Unit (PHRU), School of Clinical Medicine, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg 2000, South Africa
4. Charles River Medical Group, Harare, Zimbabwe
5. GeoPoll, 3000 Lawrence Street, Suite 125, Denver, CO 80205, USA
6. Department of Pediatrics, Vagelos College of Physicians and Surgeons, Columbia University, New York, NY 10032, USA
7. Institute for Social and Economic Research and Policy, Columbia University, New York, NY 10027, USA
8. Health Systems Research Unit, South African Medical Research Council, Bellville 7538, South Africa