Flu vaccines linked to 40% reduced risk of Alzheimer's disease

• Worldwide, there are more than 55 million people living with Alzheimer’s disease or other dementias and 10 million new cases every year, according to the World Health Organization.
• Vaccines are increasingly being investigated as a potential tool for reducing the risk of developing Alzheimer’s.
• A recent study has shown the flu vaccine could reduce this risk by 40% but the mechanism remains unclear.

Despite rapidly rising cases of Alzheimer’s disease, determining why some people develop this form of dementia and others don’t has remained elusive.

The risk factors, according to research, are multifactorial with genetics, lifestyle and our environment all potentially playing a role. One area that has not received much attention until fairly recently is how our immune system might affect our risk of developing Alzheimer’s disease.

Research in recent years has shown that receipt of some vaccines including BCG, a tuberculosis vaccine, and the chicken pox/shingles vaccine could lead to a reduced risk of developing Alzheimer’s disease.

Researchers have now found that the flu vaccine may have a protective effect, but it is not clear whether the vaccines themselves have an effect on risk, or whether preventing an infection does.

These results are published in the Journal of Alzheimer’s Disease.

Investigating the link

Based on previous studies that suggest flu vaccines reduce the risk of dementia, a team from The University of Texas Health Science Center in Housten, Texas, sought to investigate the link between flu vaccines and the risk of Alzheimer’s-specific dementia.

Using existing claims data from patients ages 65 years or over and free of dementia during the 6-year look-back period, they created two groups, each consisting of 935,887 patients. The first group had received the flu vaccine while the second group had not. The groups were matched with regard to baseline demographics, medications and comorbidities.

The study showed that patients who received at least one flu vaccine were 40% less likely to develop Alzheimer’s disease over the 4-year follow-up period, than those who had not received the vaccine. The risk was lowest in patients who had received a flu vaccine every year over the 6-year look-back period.

The researchers used a look-back period of 6 years as previous research has shown that at least six flu vaccines are needed to reduce the risk of Alzheimer’s disease, lead author Dr. Avram Bukhbinder told Medical News Today. He said they had reanalyzed their data to look at the effect over 4, 6, and 8 years.

“Influenza vaccination had a similar effect on Alzheimer’s risk when the look-back period was lengthened from 4 years to 8 years,” he explained.

“Prior studies of patients with serious chronic illnesses (such as chronic kidney disease) and of veterans have found an association between influenza vaccination and risk of dementia, so I wasn’t too surprised to find a similar result in this broader population of older adults in the U.S.,” he added.

His views were echoed by Dr. Nicola Veronese, senior researcher in geriatrics and internal medicine at the University of Palermo, Italy who conducted a meta-analysis of five studies that had looked at the role of flu vaccination in Alzheimer’s risk, last year.

He told MNT in an interview that the paper was confirmatory of previous research and praised the size of the cohort used.

“[I] believe that this paper was confirmatory, [as a] teacher speaking,[it] was extremely well done. [T]his topic could encourage further direct evidence regarding the role of influenza vaccinations in diseases and dementia in general,” he said.

A yet elusive mechanism

It is, however, too early to recommend getting the flu vaccine to reduce the risk of Alzheimer’s disease, said Dr. Heather M. Snyder, Alzheimer’s Association vice president of medical and scientific relations.

“More research is needed to understand the biological mechanisms behind the results in this study. For example, it is possible that people who are getting vaccinated also take better care of their health in other ways, and these things add up to a lower risk of Alzheimer’s and other dementias.”
— Dr. Heather M. Snyder

“It is also possible that there are issues related to unequal access and/or vaccine hesitancy and how this may influence the study population and the research results,” she added.

The authors propose that flu vaccines could have an impact on our innate immune system.

They explain that flu vaccination and some other vaccines “are associated with non-specific protective effects via long-term reprogramming of innate immune cells.” This could have an effect on how the body clears the substance that builds up in the brain causing Alzheimer’s or inflammatory responses.

They also suggest there is a potential interaction between the adaptive immune system and vaccination that is age-related, which is one possible explanation for the findings.

Dr. Veronese described this assertation as “more theoretical than practical.”

“We don’t have any direct evidence supporting the modification in adaptive secondaries or a primary immune system,” he added.

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