Estimating vaccination coverage in low-income countries and low-resource settings: a scoping review

Reliable vaccination coverage estimates are critical for monitoring population immunity and health system performance, yet remain particularly challenging to obtain in low‑income countries and low‑resource settings. We conducted a scoping review of methods used to estimate vaccination coverage in low‑income countries and low‑resource settings that host hard‑to‑reach, conflict‑affected, migrant, refugee, and internally displaced populations, as well as populations with limited access to care. We searched PubMed and Embase, screened 3,636 records, and included 59 articles. Data were extracted on four methodological components (sampling strategy, immunisation ascertainment, data acquisition, statistical approach) and on feasibility, reliability, and acceptability. Studies covered 64 countries but were heavily concentrated in a few settings (Ethiopia, Mali, Sierra Leone, Uganda), with limited evidence from classic humanitarian emergencies. Cluster‑based household surveys and secondary analyses of large population surveys dominated, while a minority of studies applied alternative or adapted approaches such as LQAS, network‑based sampling, capture‑recapture, and geostatistical modelling. Common challenges included weak or outdated sampling frames, incomplete home-based records, recall and information bias, and logistical constraints from conflict, geography, and limited digital infrastructure. Evidence on the performance and feasibility of hybrid or model‑based approaches in data‑poor settings remained limited. Current coverage estimates in low‑income and low‑resource settings rely heavily on cluster surveys that often struggle to capture the populations at greatest risk of under‑immunisation. There is an urgent need to develop, adapt, and evaluate context‑sensitive methods explicitly designed for insecure, mobile, and isolated populations, and to integrate community engagement and flexible sampling strategies to reduce their systematic invisibility in coverage data.

Key messages

• Cluster surveys remain the dominant tool for estimating vaccination coverage. Despite their benefits and improvements over time, they often miss hard-to-reach populations in fragile settings.

• Context-sensitive, resource-efficient methods, including innovative sampling techniques and geostatistical modelling, must be expanded to capture invisible groups and guide equitable immunisation.