Does Influenza Raise the Risk of Dementia? An Updated Meta-Analysis

Apparently, the effects may be comparable to, if not greater than, Covid-19.

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We often think of influenza as a short-term illness—fever, chills, and a few miserable days in bed. But what if a past influenza infection could increase your risk of neurodegenerative disease in the future?

In my previous article, I decoded the effect size of a prior influenza infection on the risk of Parkinson’s disease (PD). By conducting an updated meta-analysis, I estimated that a history of influenza increases the risk of PD by 2.1-fold. Given that the baseline risk of PD is low at <1%, a twofold risk may not seem alarming at first. But it does synergize and compound with other risk factors—such as age, genetics, and pesticide exposure—that can ultimately push someone past the tipping point for PD development.

This led me to another question: Could influenza also contribute to dementia like Alzheimer’s disease (AD), another common neurodegenerative disease?

What does the evidence say? Let’s take a closer look.

Methods

I first scanned PubMed, the leading biomedical literature database, using the following keywords: influenza[tiab] AND (dementia[tiab] OR Alzheimer [tiab]). The code [tiab] means searching for the term in the title or abstract. As of March 10, 2025, the search returned 332 results.

Going through all of them informed me that most studies are about the association between influenza vaccines and dementia. Surprisingly, no studies directly examined whether influenza raises the risk of dementia.

Only a few studies studied this indirectly by comparing the risk of dementia from Covid-19 vs influenza, which will form the basis of this present article. While the latest meta-analysis on this topic was published in 2025, it only scoured the literature until 9 November 2023. I then conducted an updated meta-analysis, as I did previously in “Influenza and Parkinson’s: How Big Is the Risk? An Updated Meta-Analysis.”