Protective Effect of Seasonal Influenza Vaccination in Elderly Individuals with Disability in Taiwan: A Propensity Score–Matched, Nationwide, Population-Based Cohort Study

This is the first and largest population-based cohort study to demonstrate that influenza vaccination reduced all-cause mortality and influenza-related hospitalization in elderly individuals with a disability. Purpose: To estimate the protective effect of influenza vaccination in elderly individuals with a disability by conducting a propensity score-matched (PSM), nationwide, population-based cohort study. Methods: Data from Taiwan’s National Health Insurance Research Database were used in this study. Generalized estimating equations (GEEs) were used to compare outcomes between the vaccinated and unvaccinated cohorts. The GEE logit was used to estimate the relative risks of death and hospitalization after influenza vaccination. Adjusted odds ratios (aORs) were used to estimate relative risk. Results: The matching process yielded a final cohort of 272 896 elderly individuals with a disability (136 448 individuals in each cohort). In multivariate GEE analyses, aOR (vaccinated vs. unvaccinated) and 95% confidence interval (CI) of death were 0.70 (0.68–0.72). The aORs (95% CIs) of hospitalization for influenza and pneumonia, respiratory diseases, respiratory failure, heart disease, hemorrhagic stroke, and ischemic stroke were 0.98 (0.95–1.01), 0.96 (0.94–0.99), 0.85 (0.82–0.89), 0.96 (0.93–0.99), 0.85 (0.75–0.97), and 0.89 (0.84–0.95), respectively. The length of stay and medical expenditure exhibited greater reduction in vaccinated elderly individuals with a severe and very severe disability than in unvaccinated elderly individuals. Conclusions: Influenza vaccination reduced all-cause mortality, influenza-related hospitalization, length of stay, and medical expenditure in elderly individuals with a disability. The decrease in the length of stay and medical expenditure because of influenza vaccination was proportional to the severity of disability.