Approximating vaccine delivery costs to reach zero-dose children: a Bayesian meta-regression analysis.

The Immunization Agenda 2030 calls for reaching all people with immunization services, including "zero-dose" children-children who have not received any routine vaccines. To plan and finance efforts to fully vaccinate these children and improve coverage and equity, decision-makers need reliable cost estimates. However, primary data on the costs of reaching zero-dose children, typically part of disadvantaged and hard-to-reach populations, are scarce. This study approximates these costs using standardized, country-level estimates of vaccine delivery unit costs for outreach delivery in low- and middle-income countries (LMICs). We extracted outreach delivery cost per dose estimates for childhood immunization services from the 2024 update of the Immunization Delivery Cost Catalogue. Using these data, we developed a meta-regression model to estimate standardized outreach vaccine delivery unit costs. The generalized linear model assumed a Gamma-distributed outcome with a log link and included both country-level and study-level predictors: study year, economic or financial cost basis, routine or campaign delivery, and full or incremental costing approach. The fitted model was used to estimate 2024 outreach delivery costs per dose for 129 LMICs. The model was estimated using 48 observations from 19 countries focused on outreach or mobile vaccine delivery. The best-fitting specification included diphtheria-tetanus-pertussis coverage, per capita gross domestic product, and under-five population size as predictors. For 2024, the predicted mean economic cost per dose was $8.65 (95% credible interval $2.33-23.71), averaged across all 129 LMICs. To fully immunize a zero-dose child with 13 recommended vaccinations, the equivalent cost estimate was $112.45 ($30.29-308.23). Reaching zero-dose children is crucial for improving equity in global health, and estimates of the costs of doing so are needed to inform budgeting for immunization programs. These meta-regression-based cost estimates can help countries to improve budgeting, planning, and resource allocation for efforts to reach zero-dose children.