Lower vaccine uptake amongst older individuals living alone: A systematic review and meta-analysis of social determinants of vaccine uptake.

INTRODUCTION: Vaccination is a key intervention to reduce infectious disease mortality and morbidity amongst older individuals. Identifying social factors for vaccine uptake enables targeted interventions to reduce health inequalities. OBJECTIVE: To systematically appraise and quantify social factors associated with vaccine uptake amongst individuals aged ≥60years from Europe. METHODS: We searched Medline and Embase from inception to 24/02/2016. The association of vaccine uptake was examined for social factors relevant at an individual level, to provide insight into individuals' environment and enable development of targeted interventions by healthcare providers to deliver equitable healthcare. Factors included: living alone, marital status, education, income, vaccination costs, area-level deprivation, social class, urban versus rural residence, immigration status and religion. Between-study heterogeneity for each factor was identified using I2-statistics and Q-statistics, and investigated by stratification and meta-regression analysis. Meta-analysis was conducted, when appropriate, using fixed- or random-effects models. RESULTS: From 11,754 titles, 35 eligible studies were identified (uptake of: seasonal influenza vaccine (SIV) only (n=27) or including pneumococcal vaccine (PV) (n=5); herpes zoster vaccine (n=1); pandemic influenza vaccine (n=1); PV only (n=1)). Higher SIV uptake was reported for individuals not living alone (summary odds ratios (OR)=1.39 (95% confidence interval (CI): 1.16-1.68). Lower SIV uptake was observed in immigrants and in more deprived areas: summary OR=0.57 (95%CI: 0.47-0.68) and risk ratio=0.93 (95%CI: 0.92-0.94) respectively. Higher SIV uptake was associated with higher income (OR=1.26 (95%CI: 1.08-1.47)) and higher education (OR=1.05 (95%CI: 1-1.11)) in adequately adjusted studies. Between-study heterogeneity did not appear to result from variation in categorisation of social factors, but for education was partly explained by varying vaccination costs (meta-regression analysis p=<0.0001); individuals with higher education had higher vaccine uptake in countries without free vaccination. CONCLUSIONS: Quantification of associations between social factors and lower vaccine uptake, and notably living alone (an overlooked factor in vaccination programmes), should enable health professionals target specific social groups to tackle vaccine-related inequalities.