The global population is ageing. Dementia and Parkinson’s disease are diseases that are common among older adults. Therefore, the number of patients with these two diseases is about to strongly increase in the next decades. Dementia is characterized by the impaired ability to remember, think, or make decisions. It interferes with doing everyday activities. Parkinson’s disease is a brain disorder that causes unintended or uncontrollable movements, such as shaking and stiffness. It also causes difficulty with balance and coordination. To date, there has been a lack of effective treatment options for both diseases. Prior studies have suggested that influenza, a contagious respiratory illness caused by influenza viruses that infect the nose, throat, and sometimes the lungs, may increase the risk of dementia and of Parkinson’s disease. Therefore, influenza vaccines earlier in life could lower the risk of developing dementia and Parkinson’s disease later. However, the quality of the studies in the area is limited. Moreover, these studies focused on vaccinations in older adults. Using a large database from the United Kingdom, we will compare the rates of dementia and of Parkinson’s disease between people with and without vaccination for influenza between 40 and 50 years of age. We hope that the findings from this study will provide needed insight on the role of influenza vaccinations in dementia and Parkinson’s disease. This would then inform the development of vaccination programs to reduce the number of patients affected by these diseases.
Given the ageing population, the prevalence of dementia and Parkinson’s disease (PD) is projected to increase in the upcoming years. Previous pre-clinical and observational studies have suggested that past infections such as influenza play a role in the pathophysiology of these conditions. Therefore, immunizations for influenza could have beneficial effects regarding the prevention of neurodegenerative diseases later in life. However, available evidence in this regard is limited. On the one hand, prior observational studies on the effects of influenza vaccines on the risk of dementia or PD had several methodological limitations. On the other hand, these studies focused on immunizations occurring later in life. This precludes conclusions on their potential effects when occurring earlier in life, when the pathophysiologic cascade that ultimately leads to neurodegenerative diseases has not yet begun. Our hypothesis is that early immunizations for influenza could be associated with decreased risks of dementia and PD. To investigate these potential associations, we will conduct a cohort study including all patients in the United Kingdom’s Clinical Practice Research Datalink (CPRD) Aurum between 40 and 50 years of age from 1 January 1996 to 31 December 2022. Each individual receiving an influenza vaccine will be matched 1:1 on calendar month, age, sex, and CPRD general practice to individuals not exposed to the influenza vaccine. Using a modified intention-to-treat exposure definition with a two-year lag period, we will compare the risk of dementia and PD between exposed and unexposed individuals. Cox proportional hazards models will calculate hazard ratios and 95% confidence intervals, adjusted for confounders at baseline. In secondary analyses, we will assess potential effect modifications by age, sex, number of influenza vaccines, time since first influenza vaccine, and seasonality. Sensitivity analyses will assess the potential impact of different sources of bias.
Dementia, Parkinson’s disease
Samy Suissa - Chief Investigator - Sir Mortimer B Davis Jewish General Hospital
Paul Brassard - Corresponding Applicant - McGill University
Antonios Douros - Collaborator - McGill University
Sophie Dell'Aniello - Collaborator - McGill University
Ying Cui - Collaborator - Sir Mortimer B Davis Jewish General Hospital
Practice Level Index of Multiple Deprivation