For decades, vaccines have been developed to prevent infectious disease. But what if some vaccines do more than that? What if they can also influence how our bodies protect us from other diseases? Could vaccines help prevent dementia?
A series of surprising studies now suggest that the shingles and RSV vaccines may be associated with a reduced risk of developing dementia. While this research is still emerging and does not yet prove cause and effect, it is opening up fascinating new questions about the connections between the immune system and brain health.
An Unexpected Clue from Health Records
The story began when researchers noticed a unique opportunity to study people in Wales, UK, who were just old enough to receive a shingles vaccine and those who narrowly missed eligibility due to age cutoffs. Because these groups were otherwise very similar, they provided an unusually clean comparison.
When scientists followed these individuals over time, they made an unexpected observation: people who received the shingles vaccine were significantly less likely to later be diagnosed with dementia. Additional studies have strengthened the link between shingles vaccine and lower dementia risk.
How is Shingles Different?
To understand why a shingles vaccine might influence brain health, it helps to know a bit about the virus it targets. Shingles is caused by varicella-zoster virus, the same virus that causes chickenpox. After a person recovers from chickenpox, the virus doesn’t fully leave the body. Instead, it can remain dormant, or inactive, in nerve cells for decades.
As we age, our immune system gradually becomes less responsive, a process sometimes called immunological aging. This makes it easier for dormant viruses to reactivate. When reactivation occurs in nerves outside the brain and spinal cord, it can lead to the painful rash we know as shingles.
Our nerves are closely linked to structures near the brain, raising the possibility that the repeated reactivation of viruses could contribute to inflammation that affects the brain as well.
Boosting Immune Memory
One straightforward explanation for how the shingles vaccine is associated with dementia is improved immune control. Shingles vaccines are designed to boost immune memory against varicella-zoster virus, helping the immune system keep the virus suppressed. Better control of viral reactivation could mean less chronic inflammation affecting nerve cells over time.
Chronic inflammation has long been suspected as a contributor to neurodegenerative diseases like dementia. If a vaccine helps reduce one source of that inflammation—even indirectly—it could potentially lower long-term risk.
A Clue Hidden in Vaccine Ingredients
Another intriguing insight comes from studies comparing different vaccines. Recent analyses have found that people who received the shingles vaccine (and in some cases the RSV vaccine) had lower dementia risk than those who received influenza vaccines.
One key difference is that the shingles and RSV vaccines share a powerful immune-stimulating ingredient called an adjuvant. Adjuvants are added to some vaccines to enhance the immune response, particularly in older adults whose immune systems may need an extra push.
These adjuvants strongly activate the innate immune system—the body’s first line of defense. Emerging research suggests that this activation can leave a kind of “imprint” on immune cells, temporarily changing how they respond to future challenges. Scientists sometimes refer to this as “trained immunity.”
Rather than lasting for a lifetime, these changes may persist for weeks or months, subtly shifting the immune system’s baseline state. That shift could influence inflammation throughout the body, including in the brain.
What This Means—and What It Doesn’t (Yet)
Let’s be clear, these findings do not mean that the shingles vaccine is a proven treatment or guaranteed prevention for dementia. The evidence so far comes from observational studies, which can show relationships but not definitive causes. That said, the consistency of the findings across different populations, coupled with the plausible biological explanations, make this a compelling area for further research.
Future studies may track immune markers in vaccinated and unvaccinated individuals, explore how inflammation in the brain changes over time, and test whether specific immune pathways are responsible for the observed protection.
A New Way of Thinking About Vaccines
At a time when vaccines are often discussed only in terms of risks or side effects, these findings offer a powerful reminder of their potential benefits—some of which we are only beginning to understand. As immunologists continue to explore the deep connections between the immune system and the brain, studies like these may open the door to entirely new strategies for preventing neurodegenerative disease in the future.
