An extensive systematic review and meta-analysis have provided good evidence that adult vaccines significantly reduce the risk of dementia and Alzheimer’s disease. This offers more reasons than ever for adults to keep up with the adult vaccination schedule.

More and more evidence suggests that certain pathogenic infections may increase the risk of dementia and Alzheimer’s disease.

Let’s take a look at this new paper that links adult vaccines to a lowered risk of dementia and Alzheimer’s disease.

What is Alzheimer’s disease?

Before I proceed, it’s important to describe Alzheimer’s disease (AD). It is a chronic neurodegenerative disease that usually starts slowly and worsens over time. It accounts for 60-70% of dementia cases, even though the terms are sometimes used interchangeably. Alzheimer’s disease is a form of dementia.

Amyloid plaques, phosphorylated tau tangles, and neurofibrillary tangles are generally easily visible pathologies that can be observed by microscopic analysis of brain tissue from autopsies of those potentially afflicted by AD. These plaques and tangles seem to affect nerve functioning. Despite these observations, the precise pathophysiology, or development, of the disease is not known.

Since amyloid plaques are often identified in patients with Alzheimer’s disease, a large amount of research is focused on attacking those plaques as a way to reverse the effect on nerves which leads to AD.

The causes of AD are unknown (notice how much we do not know about this disease), although it is speculated that it is mostly genetically related, with a large number of genes that underlie this relationship. Despite the internet tropes, there is no rigorous evidence that aluminum causes AD – I wish this belief went away fast.

And since we have no clear understanding of the etiology and pathophysiology of AD, there are few treatments available today for the disease. Some drugs target the amyloid plaques but have not been shown to change the outcomes of AD.

There are a couple of medications that help manage some of the symptoms of the disease, but they are certainly not cures. There are several drugs at the very earliest stages of development that may hold out hope to treat the underlying disease.

One more thing that needs to be made clear. There are no biological tests for Alzheimer’s disease — usually, you can only find the amyloid plaques and other pathologies in post-mortem autopsies. Unfortunately. in the absence of an autopsy, clinical diagnoses of AD are “possible” or “probable”, based on other findings, such as memory tests and other methods.

The adult vaccines and dementia risk paper

In a paper published on 3 May 2022 in Frontiers of Immunology, the researchers completed a systematic review and meta-analysis (considered the top of the hierarchy of biomedical research) of 17 studies that included 1,857,134 participants. This study had a large patient population which improves statistical significance.

All vaccine types were associated with a reduced risk of dementia. Here are some of the more significant results:

• The rabies vaccine resulted in a 57% reduction in the risk of dementia. I need to state a note of caution about this result — the rabies vaccine is rarely given to individuals unless they have potential exposure to rabies. It is not a part of the adult vaccination schedule unless a person has a high risk of exposure to rabies.
• Tdap, which is the adult vaccine for tetanus, diphtheria, and pertussis (whooping cough), resulted in a 31% reduction in the risk of dementia. There is a clinical trial (NCT05183516) that is currently recruiting older adults to confirm the link between Tdap and a lowered risk of dementia.
• The Herpes zoster vaccine (for shingles) also showed a 31% reduction in the risk of dementia. A large study also showed a similar decrease in risk.
• Annual influenza vaccinations showed a 26% reduction in the risk of dementia. One study showed a 40% reduction in risk.
• The hepatitis A vaccine showed a 22% reduction in risk.
• The hepatitis B vaccine showed an 18% reduction in risk.
• Those who had received four or more adult vaccines exhibited a 49% reduction in the risk of dementia.
• Gender and age did not affect the reduction of risk, it was just the type and number of vaccines.

Summary of adult vaccines and dementia risk

This was a large systematic review and meta-analysis that provided strong evidence that adult vaccines were linked to a statistically significant reduction in the risk of dementia and Alzheimer’s disease. I am so impressed by this study that I’m giving it 4.5 out of five stars.

Now, there are a couple of caveats that I need to make with this type of study. First, it is possible that confounders may influence the result. It is possible that vaccinated individuals take better care of their overall health, and it’s not just vaccines that lower the risk. Second, I still have read a good paper that describes the reasons why pathogenic infections might be linked to a higher risk of dementia.

However, there is a growing body of evidence that there is a causal link between adult vaccines and a lower risk of neurodegenerative diseases, such as dementia and Alzheimer’s disease.

Based on the evidence presented in this paper, I am strongly urging everyone to keep up with the adult vaccination schedule.

Citations

• Bukhbinder AS, Ling Y, Harris K, Jiang X, Schulz PE. Do vaccinations influence the development of Alzheimer disease? Hum Vaccin Immunother. 2023 Jun 8:2216625. doi: 10.1080/21645515.2023.2216625. Epub ahead of print. PMID: 37291109.
• Ecarnot F, Boccardi V, Calcagno A, Franceschi C, Fülop T, Itzhaki RF, Michel JP, Panza F, Rainero I, Solfrizzi V, Ticinesi A, Veronese N, Maggi S. Dementia, infections and vaccines: 30 years of controversy. Aging Clin Exp Res. 2023 Jun;35(6):1145-1160. doi: 10.1007/s40520-023-02409-8. Epub 2023 May 9. PMID: 37160649; PMCID: PMC10169152.
• Wu X, Yang H, He S, Xia T, Chen D, Zhou Y, Liu J, Liu M, Sun Z. Adult Vaccination as a Protective Factor for Dementia: A Meta-Analysis and Systematic Review of Population-Based Observational Studies. Front Immunol. 2022 May 3;13:872542. doi: 10.3389/fimmu.2022.872542. PMID: 35592323; PMCID: PMC9110786.