1. Center for Global Health, Global Immunization Division, Centers for Disease Control and Prevention, Atlanta, GA 30329, USA
2. Department of Disease Control and Prevention, Public Health Division, Ghana Health Service, Accra 00233, Ghana
3. Navrongo Health Research Centre, Health Research Division, Ghana Health Service, Navrongo 03821, Ghana
4. African Field Epidemiology Network, Kampala 10102, Uganda
5. Ghana Field Epidemiology and Laboratory Training Programme, School of Public Health, University of Ghana, Accra 00233, Ghana