Annual revaccination against influenza and mortality risk in community-dwelling elderly persons

Abstract

Context: Although large-scale observational studies have demonstrated the effectiveness of influenza vaccination, no large studies have systematically addressed the clinical benefit of annual revaccinations.

Objective: To investigate the effect of annual influenza revaccination on mortality in community-dwelling elderly persons.

Design, setting, and participants: A population-based cohort study using the computerized Integrated Primary Care Information (IPCI) database in the Netherlands including community-dwelling individuals aged 65 years or older from 1996 through 2002. For each year, we computed the individual cumulative exposure to influenza vaccination since study start.

Main outcome measure: Association between the number of consecutive influenza vaccinations and all-cause mortality vs no vaccination after adjusting for age, sex, chronic respiratory and cardiovascular disease, hypertension, diabetes mellitus, renal failure, and cancer.

Results: The study population included 26,071 individuals, of whom 3485 died during follow-up. Overall, a first vaccination was associated with a nonsignificant annual reduction of mortality risk of 10% (hazard ratio [HR], 0.90; 95% confidence interval [CI], 0.78-1.03) while revaccination was associated with a reduced mortality risk of 24% (HR, 0.76; 95% CI, 0.70-0.83). Compared with a first vaccination, revaccination was associated with a reduced annual mortality risk of 15% (HR, 0.85; 95% CI, 0.75-0.96). During the epidemic periods this reduction was 28% (HR, 0.72; 95% CI, 0.53-0.96). Similar estimates were obtained for persons with and without chronic comorbidity and those aged 70 years or older at baseline. Overall, influenza vaccination is estimated to prevent 1 death for every 302 vaccinees at a vaccination coverage that varied between 64% and 74%.

Conclusion: Annual influenza vaccination is associated with a reduction in all-cause mortality risk in a population of community-dwelling elderly persons, particularly in older individuals.