Alzheimer’s disease is a progressive neurological disorder that causes brain atrophy and brain cells to die. The part of the brain associated with learning is typically affected first, so early symptoms include memory issues and impaired judgement or reasoning. Severe cognitive difficulties and memory impairments ensue as the condition worsens with time. As the person enters the final stage of the disease, continuous assistance is required to carry out daily tasks.

The exact cause of Alzheimer’s disease is still being studied and not yet fully understood; however, increasing age is thought to be one of the risk factors. Alzheimer’s disease is most common amongst those 65 years and older. In the US, there are an estimated 2.2 million diagnosed prevalent cases of Alzheimer’s disease in men and women 60 years and older and that number is estimated by GlobalData epidemiologists to increase to 3 million by 2028 (as shown in Figure 1). There is no cure for Alzheimer’s disease yet; however, promising results from a study led by Bukhbinder and colleagues showed that the flu vaccine offers some protective benefits in reducing the risk of developing the disease in the elderly population, who are the most vulnerable.

The nationwide retrospective cohort study conducted in the US was published in the Journal of Alzheimer’s Disease, in which researchers used medical claims data to assess whether flu vaccination offered protection against the risk of incident Alzheimer’s disease in those 65 years and older. Patient claims data from 2009 to 2019 were obtained from a medical insurer, and propensity-score matching was applied to give two cohorts of participants with similar demographics.

The flu-vaccinated and non-vaccinated cohorts had a sample size of 935,887 individuals who were 65 years and older and free of dementia during the six-year look-back period. In the follow-up period, from 2015 to 2019, researchers found that 5.1% of patients with at least one flu vaccine had developed Alzheimer’s disease compared to 8.5% of the non-flu-vaccinated patients. This means that patients 65 years and older with at least one flu vaccine were 40% less likely than their non-flu-vaccinated peers to develop incident Alzheimer’s disease in the follow-up period. However, it is important to note that adults who have the flu vaccine are more likely to have had other vaccinations and engage in positive health-seeking behaviours, so it is possible the protective benefits offered by the flu vaccine are partially confounded by other factors not accounted for in this study.

The findings from Bukhbinder’s team are promising, but not conclusive. More research is still needed to validate the results from this finding and further deepen our understanding of why the influenza vaccine has shown protective benefits against developing Alzheimer’s disease. This area of research could become increasingly important to explore as the ageing population in the US continues to grow, as will the pool of individuals prone to developing Alzheimer’s disease. Additionally, studying the same research outcomes with the Covid-19 vaccine would be worth investigating to understand the immune system’s response to different vaccinations and its association with Alzheimer’s disease.