Small-area variation in child under-vaccination in India: a multilevel analysis of cross-sectional data from 36 states and Union Territories, 707 districts, and 22,349 small-area clusters.

Background: India has made exceptional advances in child immunisation, but subnational inequities in vaccination coverage impede attainment of key programmatic goals. Our study provides an up-to-date national portrait of local variations in child vaccination using a comprehensive set of indicators relevant to routine immunisation. Methods: Indicators representing unvaccinated (zero-dose) children, incomplete basic immunisation, and vulnerability to measles and polio, were constructed from India's 2019-2021 National Family Health Survey. We used four-level random effects logistic regression models to partition the total outcome variation over state, district and cluster levels, and produce precision-weighted estimates of prevalence across clusters. District-level prevalence and within-district variation using standard deviation measures were derived for each outcome. Boxplots graphically summarised the distribution of precision-weighted mean cluster prevalence by state. Findings: The analysis included 87,622 children aged 12-36 months. Clusters accounted for 67.6% (var: 1.36; SE: 0.127) of the variation among zero-dose children, and more than 50% for all indicators. Districts with a higher prevalence of under-vaccination tended to have higher within-district heterogeneity, interpretable as greater within-district child vaccination inequities. For vaccines administered in the first year of life, the northeastern states and Uttar Pradesh had the highest median under-vaccination. Despite India's high aggregate vaccine coverage, the distribution of small-area (cluster) mean prevalence highlighted pockets of low coverage in most states, suggesting ongoing vulnerability to measles and polio. Interpretation: Achieving India's vaccination goals requires a strategic shift towards identification and targeting of low-immunity clusters at the sub-district level. Funding: Canadian Institutes of Health Research.