1. Department of International Health, Johns Hopkins Bloomberg School of Public Health , 615 N Wolfe Street, Baltimore, MD 21205, United States
2. Department of International Health, Johns Hopkins Bloomberg School of Public Health , 415 N Washington Street, Baltimore, MD 21205, United States
3. National Vaccines and Immunization Program, Ministry of Health Kenya , Afya House, Cathedral Road, P. O. Box 43319–00100, Nairobi, Kenya
4. Jhpiego Kenya , 2nd Floor, Arlington Block, 12 Riverside, off Riverside Drive, P.O. Box 66119-00800, Nairobi, Kenya