Determinants of low vaccination uptake among older adults in Türkiye: a cross-sectional study, 2023

Background

Vaccination against influenza and pneumococcal disease is essential to reduce morbidity and mortality among older adults; however, uptake remains suboptimal. This study aimed to identify determinants of vaccination among individuals aged ≥65 years in Türkiye using both traditional statistical methods and machine learning(ML) approaches.

Methods

This cross-sectional study utilized data from the 2023 Türkiye Elderly Profile Survey (n = 11,657). Multivariable logistic regression analyses were performed to identify factors associated with vaccination. In parallel, machine learning models were developed, and class imbalance was addressed using SMOTE. Model performance was evaluated using stratified 10-fold cross-validation and an independent test set (ROC-AUC, precision, recall, F1-score). Feature importance was assessed using SHAP values.

Results

Vaccination coverage was 19.4% for influenza and 3.6% for pneumococcal vaccination. Individuals aged ≥75 years had higher odds of influenza vaccination (OR = 1.47, 95% CI:1.29–1.68), as did those with chronic disease (OR = 1.63, 95% CI:1.41–1.88) and university education (OR = 1.61, 95% CI:1.36–1.91). Living alone was associated with lower influenza vaccination (OR = 0.86, 95% CI:0.76–0.99). For pneumococcal vaccination, higher education and older age were also among the strongest predictors. ML models showed modest predictive performance (ROC-AUC:0.57–0.60) and did not outperform logistic regression. Feature importance analyses consistently identified age, education, chronic disease, healthcare utilization, functional independence, and regional disparities as key determinants.

Conclusions

Vaccination uptake among older adults in Türkiye remains low, particularly for pneumococcal vaccination. ML did not improve predictive performance but confirmed the robustness of key determinants. Targeted strategies addressing socioeconomic inequalities and strengthening primary care access are needed to improve vaccination coverage.

Key messages

• Vaccination uptake among older adults in Türkiye is low, with strong inequalities linked to age, education, and health status.

• Interventions targeting vulnerable groups and improving primary care engagement are essential to increase vaccination coverage.