1. Makerere University, Department of Population Studies, P.O. Box 7062, Kampala, Uganda
2. Department of Population and Family Health, Mailman School of Public Health, Columbia University, 60 Haven Avenue, Suite B2, New York, NY 10032, USA
3. Partnership for Reviving Routine Immunization in Northern Nigeria (PRRINN) and Maternal, Newborn and Child Health (MNCH) Programme, Abia State House, Abuja, Nigeria