Individuals with type 1 diabetes, type 2 diabetes requiring insulin or oral hypoglycaemic drugs, or diet controlled diabetes are among the clinical risk groups recommended to receive annual influenza immunisation in the UK. The authors of this research note however that there is limited evidence for the effectiveness of such vaccination in adults of working age, and their population-based cohort study was designed to investigate this further.
The study was conducted in Canada and involved all adults with diabetes identified from administrative data from 2000 to 2008, 58% of whom were of working age (<65 years). They were matched by age and sex to controls without diabetes and the effectiveness of influenza vaccination on various outcome measures was estimated (total of 543,367 person-years of follow-up).
In adults with diabetes who were of working age, influenza vaccination had no apparent effect on influenza-like illnesses, but was associated with relative reductions in pneumonia and influenza hospitalisations (43%, 95% CI 28% to 54%) and all-cause hospitalisations (28%, 95% CI 24% to 32%). Vaccine effectiveness was similar in elderly adults for hospitalisations, and elderly patients additionally had reductions in influenza-like illnesses.
The researchers conclude that their findings support vaccination of working age adults with diabetes. However, the results were replicated in analyses conducted outside of influenza season, and this suggests that residual confounding was present. For example, vaccinated individuals may have been healthier and more health seeking than their unvaccinated counterparts. They conclude that randomised trials would be required to produce definitive estimates of vaccine efficacy.