Timeliness of vaccine administration among children in urban informal settlements in Nairobi, Kenya

Abstract

Timeliness of vaccination among children in urban informal settlements is understudied in sub-Saharan Africa. We determined the proportion of children below 5 years who received vaccines on time and the associated factors in two large urban informal settlements in Nairobi, Kenya. We conducted an analytic cross-sectional study in Viwandani and Korogocho, randomly selected households with a child below 5 years, and administered questionnaires to mothers/caregivers. Timely vaccination was defined according to the Kenya Expanded Programme on Immunization schedule. Vaccination was considered timely if administered within 28 days of birth for Bacille Calmette-Guérin (BCG), between 14 and 18 weeks for Diphtheria-Tetanus Pertussis-Haemophilus influenzae type b-Hepatitis B dose 3 (DTP-Hib-HepB-3), and between 9 and 10 months for Measles-Containing Vaccine dose 1 (MCV1). Multivariable modified Poisson regression identified the factors associated with timely vaccination. Of 412 children, 216 (52%) with verifiable immunization booklets were analyzed for timeliness. Timely vaccination rates were 90.4% for BCG (189/209), 90.2% for DTP-HIB-Hep-3 (184/204), and 84.2% for MCV1 (160/190). Factors associated with timely vaccination included caregiver uncertainty about access to health services, which reduced the likelihood of timely BCG (adjusted prevalence risk ratio [aPR] 0.87, 95% confidence interval [CI] 0.78-0.96), DTP-Hib-HepB-3 (aPR 0.88, 95% CI 0.79-0.98), and MCV1 (aPR 0.81, 95% CI 0.70-0.94). Compared with Korogocho, children in Viwandani were more likely to receive timely MCV1 (aPR 1.18, 95% CI 1.03-1.35), whereas children of Christian caregivers were less likely than those of non-religious caregivers (aPR 0.83, 95% CI 0.70-0.99). Overall, vaccination timeliness varied by antigen, with a slight decline over time for later-schedule vaccines such as MCV1. Residence, religion, and access to routine health services were key determinants of timely vaccination. Strengthening outreach, faith-based engagement, and reminder systems in informal settlements like Korogocho could enhance vaccine timeliness, particularly for vaccines administered later in infancy.