You’ve probably heard it from both directions. Someone tells you that vaccines may protect the brain. Someone else warns you they cause harm. Neither claim, stated that simply, reflects what the research shows.

What a growing body of observational research does show is this: older adults who receive certain routine vaccines, particularly influenza and shingles vaccines, tend to develop dementia at lower rates than those who do not. The word to hold onto is ‘tend.’ These are associations, not proof of cause and effect.

At the same time, no credible study has found that vaccines increase dementia risk. That claim, which circulates widely in certain corners of the internet, is not supported by the evidence.

This article explains what the research found, what it didn’t prove, and what the signal likely means for caregivers thinking about preventive health.

Most of this research was conducted in people before a dementia diagnosis, during the years when the disease is developing but not yet visible. If your Tended (the person you’re caring for) has already been diagnosed, the primary findings about dementia prevention are less directly applicable. The underlying message, however, still matters.

Serious infections accelerate cognitive decline in people already living with dementia. A severe flu, a shingles outbreak, hospitalization with delirium. Each of these events is associated with measurable worsening. Keeping your Tended current on recommended vaccines is standard preventive care, supported by their physician, for reasons that go well beyond dementia.

For caregivers themselves, the research carries a separate reminder. Caregiver health is easy to defer and hard to recover. Vaccination, regular medical care, and reducing infection exposure are not luxuries. They are part of a sustainable caregiving life.

The most cited study in this area, Bukhbinder et al. published in the Journal of Alzheimer’s Disease in 2022, compared nearly 936,000 matched pairs of adults aged 65 and older. Those who had received an influenza vaccine had a 40 percent lower relative risk of developing Alzheimer’s disease over four years of follow-up. The study used propensity score matching, a statistical technique designed to make the vaccinated and unvaccinated groups as comparable as possible.

The shingles research is arguably more compelling. A 2024 study by Taquet and colleagues, published in Nature Medicine, used a natural experiment created when the United States rapidly switched from the old live-attenuated shingles vaccine to the recombinant Shingrix vaccine in October 2017. Among more than 103,000 matched individuals, those who received the recombinant vaccine had a 17 percent increase in diagnosis-free time. Among those who eventually developed dementia, this translated to approximately 164 additional days lived without a dementia diagnosis.

The most methodologically rigorous work to date comes from Eyting and colleagues, published in Nature in 2025. Using an age-based eligibility cutoff in Wales and Australia as a natural experiment, the researchers found that the live-attenuated shingles vaccine reduced dementia occurrence by approximately 20 percent. They also found that vaccination reduced both mild cognitive impairment diagnoses and deaths from dementia. Age-cutoff designs like this one approximate randomization because they compare people on either side of an arbitrary age boundary, making the groups nearly identical except for vaccine eligibility.

Individual studies can reflect chance. Systematic reviews, which pool results across multiple studies, provide sturdier ground.

A 2022 meta-analysis by Veronese and colleagues in Ageing Research Reviews examined five cohort studies with nearly 292,000 participants. Influenza vaccination was associated with reduced dementia risk in high-risk populations, and the signal strengthened with more annual doses. People who received four or more annual flu vaccines had a 57 percent lower hazard of developing dementia compared to unvaccinated individuals.

A broader systematic review by Wang and colleagues, published in Frontiers in Immunology in 2024, examined multiple vaccine types including influenza, herpes zoster, pneumococcal, and Tdap vaccines. The pattern was consistent across all of them: vaccination associated with lower dementia incidence. This consistency across different vaccines and different pathogens is biologically informative. It suggests the mechanism may be less about any specific pathogen and more about the broader immune and inflammatory response.

Researchers have proposed several mechanisms that could explain why vaccination might protect the brain.

Serious infections, including flu and shingles, trigger systemic inflammation. Inflammation reaches the brain. In older adults, this inflammatory cascade is associated with delirium, accelerated cognitive decline, and increased dementia risk. Vaccines reduce the likelihood and severity of these infections, which may protect the brain indirectly by preventing inflammatory cascades and their downstream consequences.

In the case of shingles specifically, the varicella-zoster virus establishes lifelong latency in nerve cells. Reactivation, even subclinically without visible rash, triggers neuroinflammation and has been linked to amyloid deposition and tau aggregation, two hallmarks of Alzheimer’s disease pathology. Preventing reactivation through vaccination may blunt this chronic inflammatory burden.

The adjuvant hypothesis is newer and more speculative. A 2025 study by Taquet’s group found that the AS01 adjuvant, an immune-stimulating ingredient in Shingrix, was associated with lower dementia risk independent of the vaccine’s antigen. The same adjuvant is used in a respiratory syncytial virus vaccine, and that vaccine showed a similar association. If confirmed, this would suggest that certain immune activation patterns, not just infection prevention, may directly influence brain aging.

Note: The adjuvant hypothesis is preliminary. It requires replication before it can be taken as more than a signal worth investigating.

Science is as much about what we cannot yet claim as what we can. Here is where the evidence falls short of the claims sometimes made in headlines.

• Vaccines have not been proven to prevent dementia. The available studies are observational. They show that vaccinated people develop dementia less often. They do not establish that vaccination caused that difference.
• Healthy vaccinee bias is a real and unresolved limitation. People who seek out vaccines tend to be more health-conscious, better resourced, and generally healthier than those who do not. No observational study can fully account for this. Natural experiment designs (like the age-cutoff studies) come closest to resolving it, but they too have limitations.
• No randomized controlled trial has tested any vaccine as a dementia prevention strategy. Without that trial, we cannot make the causal claim. The associations are consistent and biologically plausible, but consistent and plausible is not the same as proven.
• Vaccines have not been shown to cause dementia. No well-designed study demonstrates an increased dementia risk from any recommended adult vaccine. The claim that vaccines cause Alzheimer’s disease is not supported by the scientific evidence.

The research on vaccines and dementia risk is genuinely interesting, and it is growing. Multiple large studies consistently show that vaccinated older adults develop dementia at lower rates. The shingles vaccine research, particularly the natural experiment work, produces the most methodologically rigorous signal. The flu vaccine research is large in scale but more susceptible to healthy vaccinee bias.

None of this research was designed to test dementia prevention. None of it proves that vaccination will protect any individual’s brain. What it does suggest is that serious infections accelerate cognitive aging, and that reducing the frequency and severity of those infections through routine vaccination is reasonable care.

The decision about which vaccines are appropriate for your Tended depends on age, health status, medications, and medical history. It belongs in a conversation with your physician, grounded in standard preventive care guidelines, not in dementia-prevention claims the science hasn’t yet earned.

For caregivers tracking every piece of research that might help, this one is worth knowing. It is not a silver bullet. It is one small piece of a picture that is still being drawn.

Gregg

1. Bukhbinder AS, et al. Risk of Alzheimer’s disease following influenza vaccination: a claims-based cohort study using propensity score matching. Journal of Alzheimer’s Disease. 2022;88(3):1061-1074. PMID: 35723106.
2. Taquet M, Dercon Q, Todd JA, Harrison PJ. The recombinant shingles vaccine is associated with lower risk of dementia. Nature Medicine. 2024;30:2777-2781. PMID: 39053634.
3. Eyting M, et al. A natural experiment on the effect of herpes zoster vaccination on dementia. Nature. 2025. https://doi.org/10.1038/s41586-025-08800-x
4. Veronese N, et al. Influenza vaccination reduces dementia risk: a systematic review and meta-analysis. Ageing Research Reviews. 2022;73:101534. PMID: 34861456.
5. Wang Y, et al. Association between vaccinations and risk of dementia: a systematic review and meta-analysis. Frontiers in Immunology. 2022;13:872542. PMC: PMC12636520.
6. Taquet M, et al. Lower risk of dementia with AS01-adjuvanted vaccination against shingles and respiratory syncytial virus infections. npj Vaccines. 2025. PMID: 40562756.
7. Cunningham C. Microglia and neurodegeneration: the role of systemic inflammation. Glia. 2013;61(1):71-90. Note: verify current URL; PMC7104993 link in original article appears to reference a different paper.