GLOBAL IMPACT OF IMMUNIZATION PROGRAMMES ON CHILD MORTALITY REDUCTION: A MODELLING STUDY

Background: The Expanded Programme on Immunization, launched by the World Health Organization in 1974, is a cornerstone global health initiative aimed at reducing vaccine-preventable diseases and mortality. Its progressive expansion has improved child survival and population health. Objective: To evaluate the long-term impact of immunization programmes on mortality reduction, life-years gained, and overall health outcomes globally from 1974 to 2024. Methods: This modelling study integrates multiple transmission and static disease models to estimate vaccination impact across fourteen infectious diseases in 194 countries. Vaccine coverage data were compiled from global datasets, with regression-based imputation addressing missing values. Key outcomes included deaths averted, life-years gained, disability-adjusted life years (DALYs), and reductions in infant mortality. Time-series regression and Markov chain Monte Carlo methods were used to capture uncertainty and non-linear effects. Results: Immunization programmes are estimated to have prevented 154 million deaths, with 95% among children under five. Vaccination contributed to about 9 billion life-years gained and over ten billion years of healthy life. Measles vaccination was the leading contributor to mortality reduction. Overall, immunization accounted for around 40% of the global decline in infant mortality, with greater absolute benefits in high-burden regions. Survival probabilities improved significantly across all age groups. Conclusion: Immunization remains one of the most effective and equitable public health interventions. Sustaining progress requires continued investment, strengthened primary health care integration, and expanded life-course vaccination strategies aligned with Immunization Agenda 2030.