Determinants of influenza vaccination uptake among older adults in Catalonia using a longitudinal population study: the role of public health campaigns.

Introduction: This study examines the impact of influenza vaccination campaigns on the probability of immunisation among older adults in Catalonia, Spain. Methods: A population-based cohort study was conducted using the Catalan administrative and health dataset. Longitudinal data on healthcare resource use for individuals born before 1965 in Catalonia were used to compute descriptive statistics and concentration measures. A Regression Discontinuity Design (RDD) was performed to calculate the jump in the probability of becoming vaccinated. The database covers administrative data from primary care, hospitalisations and emergency care in the national health system from January 2014 to October 2021. Results: Significant differences were found across age groups, gender, drug copayment levels and nationality, and these differences were corroborated through concentration measures conditioned on health status. The RDD indicates a 4.78% increase in the probability of vaccination at the age at which vaccines were offered (60 years old), with the main differences observed among individuals from lower-income levels, specific health regions and nationalities. Age, a diagnosis of influenza in the previous vaccination campaign, and particular comorbidities were factors positively associated with a higher likelihood of vaccination. Conclusions: Understanding the interplay of factors is crucial to addressing disparities and ensuring preventive measures reach vulnerable groups. Our findings have direct implications for influenza vaccination coverage among older adults, providing policymakers with valuable insights for enhancing outcomes.