Persistent immunization inequities – a review and analysis of country immunization coverage and equity assessments using the modified Tanahashi model

Despite global progress in child immunization, significant inequities persist, highlighted by the fact that 14.3 million infants did not receive their initial DTP vaccine dose in 2024, and another 5.6 million were partially vaccinated. These disparities disproportionately affect marginalized groups, with zero-dose children often clustered in vulnerable communities facing multiple forms of deprivation. Addressing these persistent barriers is an ongoing challenge that requires evidence-based strategies. This study used a secondary research method, re-examining data from 11 Coverage and Equity Assessment (CEA) reports conducted in 13 countries between 2021 and 2024. The assessments were performed by consultants hired by UNICEF to analyze inequities in immunization. Data extraction involved systematically coding the reports to identify qualitative patterns and themes of the root causes of inequity. The analysis classified these codes using UNICEF's adaptation of the Tanahashi effective coverage model/framework, which groups determinants of health service coverage into four clusters: enabling environment, supply, demand, and quality. This iterative coding approach was used to critically examine the persistence of the identified barriers. The review highlights that emerging inequities primarily centre on access and supply and are heavily influenced by local government regulations. While these can be modified, issues related to demand and quality remain, which will only be resolved after addressing barriers to accessibility and supply. Demand-side challenges stemmed from socio-cultural factors, including restrictive gender norms and limited female decision-making power, as well as parental vaccine hesitancy and misinformation. Quality-related issues included variable service readiness across facilities, particularly lower standards in government-run facilities and rural areas. Gender-based barriers, when analysed, underscored how inequities at the household and community levels restricted women's and children's access to services. Immunization inequity, viewed through the lens of effective coverage between 2021 and 2024, remains a significant challenge due to a complex interplay of systemic barriers and socio-cultural determinants. The analysis highlights persistent issues in enabling the environment, supply, demand, and quality of immunization services. Effective pro-equity immunization strategies must be context-specific and address bottlenecks in each of these determinant clusters. Further research is needed to evaluate the long-term impact of these strategies and ensure they effectively reach the most vulnerable, zero-dose, and under-immunized populations. • Our study evaluated immunization inequities using the modified Tanahashi framework. • Findings reveal that the primary drivers of inequity are access and supply barriers. • There is a need to integrate gender-transformative approaches. • There is need for targeted interventions to reduce “zero-dose” children worldwide.