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Flu vaccine linked to a 40% reduction in risk of Alzheimer’s disease

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Last updated on June 12th, 2023 at 01:32 pm

A new peer-reviewed study found that people who received at least one flu vaccine were 40% less like to develop Alzheimer’s disease compared to non-vaccinated individuals. If this doesn’t convince you to run down to your local pharmacy or your physician to get the flu vaccine, I do not know what else to convince you.

As you know, I am a big proponent of the flu vaccine mainly because the disease it prevents is much more dangerous than most people seem to think. And during this time of the COVID-19 pandemic (yes, it’s still out there), getting the flu and COVID-19 vaccines are important.

Let’s dive into this paper to see if the data is convincing, and more than that, what potential mechanisms that may link the flu or flu vaccine to the risk of Alzheimer’s disease.

vaccine text and a person wearing latex glove while holding a syringe on pink background
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The flu vaccine and Alzheimer’s disease paper

In a study published on 13 June 2022 in the Journal of Alzheimer’s Disease by UTHealth Houston researchers found that people in a large nationwide sample (n=2,356,479) of US adults 65 years and older who received at least one influenza vaccine were 40% less likely than their non-vaccinated peers to develop Alzheimer’s disease over four years.

Here are the details of the results:

  • 5.1% of patients who received a flu vaccine developed Alzheimer’s disease.
  • 8.5% of patients who did not receive a flu vaccine developed Alzheimer’s disease.
  • The relative risk for vaccinated individuals was 0.60, or a 40% reduction in the risk of Alzheimer’s disease

Interestingly, this supports other studies that show a decreased risk of Alzheimer’s disease and dementia among individuals who have had various adulthood vaccinations including Tdap (the adult vaccine for tetanus, diphtheria, and pertussis), polio, and herpes zoster (shingles).

According to first author Avram S. Bukhbinder, M.D., a recent alumnus of McGovern Medical School at UTHealth Houston, in a press release issued on June 24, 2022:

The strength of this protective effect increased with the number of years that a person received an annual flu vaccine – in other words, the rate of developing Alzheimer’s was lowest among those who consistently received the flu vaccine every year. Future research should assess whether flu vaccination is also associated with the rate of symptom progression in patients who already have Alzheimer’s dementia.

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Why?

So, why do the flu (and other) vaccines reduce the risk of Alzheimer’s disease? The authors proposed three hypotheses that may provide plausible biological mechanisms for the link:

  1. influenza-specific mechanisms, including mitigation of damage secondary to influenza infection and/or epitopic similarity between influenza proteins and AD pathology;
  2. non–influenza-specific training of the innate immune system;
  3. non–influenza-specific changes in adaptive immunity via lymphocyte-mediated cross-reactivity.

The first proposed mechanism is that influenza itself may cause some damage that leads to Alzheimer’s disease, and by preventing flu (via vaccination), there is less of that damage. The latter two mechanisms imply that the flu vaccine itself provides some non-influenza-specific changes to the immune system that protects against Alzheimer’s disease.

The latter two mechanisms may explain why other adult vaccinations are also linked to lower risks of Alzheimer’s disease. Maybe these vaccines induce something in the immune system that provides a protective effect against Alzheimer’s. Given how little we know about the development and prevention of Alzheimer’s disease, this kind of observational data could lead to a better understanding of the disease leading to prevention or cures.

Influenza infection can cause central nervous system damage from a direct viral invasion of nervous tissues or as collateral damage from the systemic immune response to peripheral infection. The authors of the paper wrote:

Neurologic complications associated with influenza infection can occur in the absence of overt CNS inflammation (e.g., lack of pleocytosis or detectable virus in cerebrospinal fluid) and comprise a range of manifestations including headache, encephalopathy, demyelination, and long-term neuropsychiatric sequelae such as depression and persistent cognitive impairment.

I could speculate that with this type of data, we could develop an “Alzheimer’s vaccine,” which stimulates that part of the immune system that seems to exhibit this protective effect. I’m sure that there is a lot of research going on. I noticed a lot of recent articles that are showing that adult vaccinations are linked to a much lower risk of Alzheimer’s disease and dementia.

One should get the flu vaccine because it prevents a disease that is much more deadly than people think. During the last “normal” flu season (the past two have been very light because of all of the public health mitigation efforts of COVID-19), nearly 28,000 people died of the flu. But if it also reduces your risk of Alzheimer’s disease, then that’s a huge bonus to getting the vaccine and preventing the flu.

This line of research is very interesting, and I plan on following it as new clinical trials and epidemiological studies are published. There is something about vaccines that seem to reduce the risks of Alzheimer’s disease, and my scientific curiosity is at its maximum. I can’t wait to find out more.

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Michael Simpson
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