A recent study showed that influenza vaccine reduces stroke and heart failure-related complications in adult diabetic patients, a high-risk group for influenza-related complications. This study further justifies the strong recommendation for influenza vaccination in older adults with chronic illnesses.
There is a lack of good clinical studies that measure the effectiveness of influenza vaccination in type 2 diabetic patients. At the same time, there is a concern of a weakened immune response in diabetic patients thereby questioning the efficacy of vaccination. To address this gap, Vamos et al. conducted a retrospective study on 124,503 diabetic adult patients using the data from the Clinical Practice Research Data Link in England from Sep 2003 to Aug 2010. They primarily investigated the effect of influenza vaccination on hospital admissions related to myocardial infarction (MI), stroke and heart failure. They also evaluated the vaccine’s effect on pneumonia or influenza and death related to any cause among this patient population.
Each year was further subcategorized into 4 time periods: pre-influenza, influenza, post-influenza, and summer, with influenza season being defined as the duration during which the weekly consultation rates for influenza-like illnesses exceeded 30 per 100,000 population. A patient was considered vaccinated after 14 days of receiving the vaccine, and follow-up time was classified into vaccinated and unvaccinated person–time periods. For each cohort year, they identified adult (≥18 yrs) patients with type 2 diabetes and extracted data regarding their vaccination status and covariate data such as age, sex, smoking status, body mass index, laboratory tests (cholesterol and glycated hemoglobin[HbA1c ]), blood pressure and number of hospital admissions during the preceding 12 months. They also recorded the presence of comorbid conditions and medications. Using appropriate statistical tools, they compared the baseline data of vaccinated and non-vaccinated patients and further analyzed the data after correction for covariates. Furthermore, they compared the data between vaccinated and non-vaccinated patients in the summer and adjusted for residual confounding if there was a difference, since no benefit was expected in the summertime due to minimal influenza activity. They also weighed in whether the vaccine targeted the circulating strains for each cohort year.
The results of the study, published in the Canadian Medical Association Journal on July 25th, 2016, demonstrated that there was a distinct benefit of vaccination in the study cohort. About 63-67% of the study cohorts were vaccinated during the study period. After adjustment for covariates and residual confounding factors, vaccination reduced the rates of hospital admissions for acute MI (19%), stroke (30%), heart failure (22%), and pneumonia or influenza (15%). It also significantly reduced the rates of death due to any cause (24%) during influenza season.
Although this is a strong study owing to a large patient population across 7 influenza seasons with the availability of key laboratory and clinical parameters, it has some limitations inherent to retrospective studies. There is a risk of missing some data owing to undiagnosed cases of outcomes or comorbidity and unrecorded medical information. The vaccinated cohorts were older and had higher rates of chronic illness. Using a residual confounding factor calculated from the summer time data may not completely eliminate this bias. Nevertheless, the study demonstrated a significant benefit of influenza vaccination and supports the national guideline’s recommendation for vaccinating adults with chronic illnesses.
Written By: Kavita M. Gupta, PhD