Relationship between annual influenza vaccination and winter mortality in diabetic people over 65 years

Influenza is an important cause of morbidity and mortality in older people, especially in those with some high-risk conditions such as diabetes mellitus. This study assessed the relationship between influenza vaccination status and winter mortality among diabetics 65 y and over during four consecutive influenza seasons.

Population-based cohort study including 2,650 community-dwelling individuals 65 y or older with diabetes mellitus followed between January 2002 and April 2005 in Tarragona, Spain. Influenza vaccination status was evaluated every year of the study and the primary endpoint was considered all-cause death during the study period. Deaths were classified as occurring within influenza periods (January-April) or non-influenza periods. The relationship between vaccination and winter mortality was evaluated by multivariable discrete-time hazard models.

Influenza immunization was associated with a reduction of 33% (95% confidence interval: 4-53) in the adjusted risk of all-cause mortality throughout the overall influenza periods 2002-2005. The attributable risk to vaccination in reducing mortality was 13.5 per 100,000 person-weeks within influenza periods, estimating that one death was prevented for every 435 annual vaccinations.

Our data confirm the benefit of influenza vaccination in reducing mortality and supports the strategy of annual vaccination in diabetics aged at least 65 y.