Global burden of varicella in children aged 5–9 y, relationship with vaccination policy indicators, and projected trends to 2030

Abstract

Varicella remains a common childhood infection worldwide. Understanding long-term trends and identifying key determinants of disease burden are essential for informing vaccination strategies and public health planning. Data were obtained from the Global Burden of Disease (GBD) 2021 study and the global varicella vaccination policy information. Extreme Gradient Boosting (XGBoost) model was trained to predict the disease burden for 2030. This model estimated the incidence, prevalence, and disability-adjusted life years (DALYs) for varicella among children aged 5-9 y worldwide. Shapley Additive exPlanations (SHAP) was employed to identify key factors and inform public health strategies. From 1990 to 2021, the rate of global incidence rose from 1,028.46/100,000 to 1,048.24/100,000, prevalence from 30.81/100,000 to 31.07/100,000, and DALYs declined from 21.09/100,000 to 12.36/100,000. By 2030, these metrics are projected to fall to 897.01/100,000, 28.96/100,000, and 11.71/100,000, respectively. From 1990 through 2030, Southeast and South Asia had the highest varicella incidence, Asian and Pacific Island nations had the highest prevalence, and sub-Saharan Africa and South Asia had the highest DALYs. SHAP identified population as the strongest predictor (mean absolute SHAP value: 0.167 for incidence and 0.103 for prevalence), and higher vaccination program tier may be associated with lower DALYs. Varicella burden among children aged 5-9 y has declined globally, but model projections indicate that regional disparities will persist. The lack of vaccination coverage and cohort-level immunization data limits interpretation of vaccine effects; future studies should incorporate both coverage and cohort exposure information to strengthen policy evaluation.