Assessing immunization system performance through coverage, dropout, and health facility density in Kenya from 2020-2024

Background Assessing immunisation coverage alone often masks inequities in service access and continuity. Analysing dropout rates between the first and third doses of the DTP vaccine (DTP1-DTP3) alongside health facility density offers a more comprehensive assessment of immunisation system performance at the subnational level. We aimed to examine the relationship between immunisation coverage, DTP1-DTP3 dropout rates and trends as well as health facility distribution across all 47 counties in Kenya. Methods We conducted a county-level ecological analysis using administrative data from 2020-2024. DTP1 and DTP3 vaccination data from the Kenya Health Information System were used to calculate coverage, dropout rates and temporal trends. Health facility density (per 10,000 population) was derived from the Kenya Master Health Facility List and national population estimates. Associations between dropout rates, immunisation coverage and facility density were assessed using linear regression, and Spearman’s rank and Pearson’s correlation coefficients. Results Average DTP3 immunisation coverage ranged from 75.3% in Wajir County to 99.2% in Makueni County with a national mean of 85.1%. Dropout rates varied widely (0.5% to 12.5%), with higher values concentrated in arid and semi-arid counties. Higher dropout was modestly associated with lower coverage (r = –0.31, p = 0.04), while the association between dropout and health facility density was weak and not statistically significant (r = 0.07, p = 0.66). Vaccination trends across counties showed generally stable coverage with temporary disruption during the COVID 19 pandemic. Conclusions Subnational disparities in immunisation performance in Kenya are best understood by jointly examining immunisation coverage, dropout, and health system access data. Health facility access may be better assessed by combining population- based metrics with geospatial methods. Strengthening health infrastructure and expanding service availability are essential to closing the remaining immunisation gaps.