Estimating geographic access to health care services for children unvaccinated against diphtheria, tetanus, pertussis across low- and middle-income countries in 2021

Achieving routine immunization for all children remains a major challenge in many low- and middle-income countries. In 2021, 18.1 million children globally missed their first dose of the diphtheria-tetanus-pertussis vaccine (DTP1), highlighting gaps in immunization and healthcare services. The Global Immunization Agenda 2030 aims for 90% coverage of essential childhood and adolescent vaccines and a 50% reduction in zero-dose children by 2030. However, national level data often obscures subnational variations, hampering the identification of unvaccinated children. Geographic access to healthcare is a key factor in vaccine uptake, but global comparative studies at the subnational level are rare, limiting our understanding of local vaccination behaviours and dynamics. This study estimates and maps the number and distribution of zero-dose children and their geographic access to healthcare services across 99 low- and middle-income countries. Using geospatial modelling approaches, we assessed geographic access to the nearest facility through two scenarios: walking and taking motorised transport. We quantified spatial inequalities of immunization at 1km spatial resolution and compared the patterns with healthcare access. Results show substantial variations, both between and within countries. Among the estimated 15.7 million zero-dose children across the studied countries, 39% lived more than one hours walking from a health facility, with Afghanistan (84%), Papua New Guinea (83%), Sudan (81%), and Cambodia (78%) showing the highest proportions. When figures were disaggregated to the district level, 33% of the districts across all 99 countries had more than 50% of their unvaccinated children living more than 2 hours from a health facility by foot. At the same time, many zero-dose children overall lived within 30 minutes of a health facility under a motorised scenario, indicating that proximity alone does not ensure vaccine uptake and that additional non-geographic barriers contribute to persistent zero-dose status. We provide a foundation for targeted vaccination strategies and interventions to bridge vaccination gaps and ensure equitable access to essential healthcare services. Assessing walking and motorised travel times highlight where geographic barriers contribute to low vaccine uptake, while also pointing to settings where other factors play a larger role. These findings show where tailored interventions such as outreach services, mobile clinics or new facility placement may be required for locations that are difficult to reach. They also highlight the need to consider local contexts where conflict, insecurity or weak health system performance limit the availability or quality of services, even when geographic access is not a major barrier. Addressing both geographic and nongeographic barriers will help ensure that the children most in need are reached, reducing vaccination gaps and improving equitable access to essential healthcare.