How a flu shot could reduce your risk for dementia

A recent study highlights the relationship between viral infections, such pneumonia caused by the flu or a case of meningitis in midlife and dementia later in life. Scientists recently reported their findings in the publication Neuron. Read on to learn how a bad case of the flu or other virus could impact your risk of developing Alzheimer’s or other neurogenerative diseases.

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By Alzheimer's Prevention Bulletin

Can having a severe bout of a common virus in middle age raise your risk for dementia later in life? Scientists have recently reported research that gives credit to this possibility.

The link between viruses and neurodegenerative diseases has been hypothesized for many years. In 2022, direct evidence supporting this theory was reported by scientists who found that people infected with Epstein-Barr virus, which causes mononucleosis, are 32 times more likely to develop multiple sclerosis than those who never had the virus. This research led scientists to study other links between common viruses and neurodegenerative diseases such as Alzheimer’s disease and Parkinson’s. 

In an article published in January 2023 in Neuron, researchers reported they had discovered 12 common viruses that increase the risk of developing six different brain degenerative (neurodegenerative) diseases. The greatest risk for Alzheimer’s disease was associated with viral meningitis, followed by flu-related pneumonia and herpes simplex virus 1.

The authors of the paper analyzed medical records from 344,000 people from the Finnish nationwide biobank, FinnGen, and 106,000 in the U.K. Biobank. All participants were age 60 and older. The authors compared the presence of a neurodegenerative disease before and after hospitalization for a serious viral infection. 

Diagnoses for the participants included flu, pneumonia, meningitis, Epstein-Barr virus, encephalitis, and chickenpox/shingles. Most of these viruses are considered neurotropic viruses – meaning the virus can enter the central nervous system and into neurons.

What are the biggest culprits for future dementia? People with viral encephalitis were 31 times more likely to develop Alzheimer’s and 40 times more likely to have a dementia of any type compared to people who were not hospitalized. Meningitis caused a 62-fold increase in risk of developing Alzheimer’s. And flu and flu-induced pneumonia were linked to the most types of neurodegenerative diseases.

The risk of dementia was highest during the first year after infection. While risk waned significantly over the next 15 years, some risk still remained.

It is important to point out that these cases were all in people who had severe symptoms and were hospitalized. Also, there was not enough data to explore the relationship between COVID-19 infection and developing a neurodegenerative disease. Vaccines that prevent severe illness may partially protect someone from developing a neurodegenerative disease. Vaccinations are available for the flu, pneumonia, human papilloma virus (HPV), COVID-19 and other viruses. While vaccines do not prevent all infections, they do dramatically reduce hospitalization rates.

The relationship between viruses and risk of dementia is an important area of future research. Although the Alzheimer’s Prevention Registry doesn’t currently have studies on this topic, we are adding new studies on a regular basis. Keep a look out for study opportunity announcements and visit our Find a Study page.