By Hendra Lukman 
An innovative approach to public health policy in Wales has provided scientists with some of the most compelling evidence to date suggesting that a widely used vaccine could offer significant protection against dementia. A groundbreaking study spearheaded by Stanford Medicine, analyzing extensive health records of older adults in Wales, has revealed that individuals who received the shingles vaccine were 20% less likely to be diagnosed with dementia over a subsequent seven-year period compared to their unvaccinated counterparts.
Published on April 2 in the prestigious journal Nature, these findings lend substantial weight to an emerging hypothesis within the scientific community: that certain viral infections, particularly those that target the nervous system, may act as catalysts for the development of dementia. Should these results be consistently replicated in future investigations, they could point towards a readily available and practical strategy for dementia prevention that is already in use.
Adding further depth to this promising line of inquiry, a parallel analysis by the same research team, detailed in Cell on December 2, has indicated an additional potential benefit of the shingles vaccine. This second study suggests that the vaccine might also play a therapeutic role for individuals already living with dementia, potentially by slowing the progression of the disease.
The Shingles Virus: A Persistent Threat
Shingles, also known as herpes zoster, is a painful and often debilitating viral illness characterized by a distinctive blistering rash. It is caused by the reactivation of the varicella-zoster virus (VZV), the same pathogen responsible for chickenpox. Following an initial infection, typically in childhood, VZV does not leave the body entirely. Instead, it lies dormant within nerve cells, where it can remain inactive for decades. In later life, particularly in individuals with weakened immune systems or as a natural consequence of aging, this latent virus can reawaken and manifest as shingles.
Dementia’s Growing Burden and the Viral Hypothesis
Globally, dementia affects an estimated 55 million people, with approximately 10 million new cases diagnosed annually. For many years, the predominant focus of dementia research has been on the accumulation of abnormal proteins, such as amyloid plaques and tau tangles, which are hallmarks of Alzheimer’s disease, the most prevalent form of dementia. However, despite considerable investment and effort, these research avenues have yet to yield effective preventative or curative treatments. This lack of progress has prompted a growing number of scientists to explore alternative contributing factors, including chronic infections by specific viruses that may inflict damage on the brain over time.
Previous observational studies, which relied on analyses of large health databases, had hinted at a correlation between shingles vaccination and a reduced incidence of dementia. However, these studies were hampered by a significant inherent limitation: selection bias. Individuals who opt for vaccination are often more health-conscious across a range of behaviors that are difficult to quantify. They may adopt healthier diets, engage in more regular physical activity, and interact more frequently with the healthcare system. These lifestyle differences, known to influence dementia risk, were typically not captured in the available medical records, making it challenging to isolate the vaccine’s true impact.
Dr. Pascal Geldsetzer, an assistant professor of medicine at Stanford Medicine and the senior author of the new study, articulated this challenge: "All these associational studies suffer from the basic problem that people who go get vaccinated have different health behaviors than those who don’t. In general, they’re seen as not being solid enough evidence to make any recommendations on."
A Rare "Natural Experiment" in Wales
Approximately two years ago, Dr. Geldsetzer identified a unique opportunity within the way Wales had implemented its shingles vaccination program. The structure of this rollout presented what researchers term a "natural experiment," a situation that closely mimicked a controlled trial and appeared to circumvent the confounding biases prevalent in earlier research. At the time of the program’s inception, Wales was utilizing a live-attenuated (weakened) form of the VZV vaccine.
The national shingles vaccination initiative commenced on September 1, 2013. The policy dictated that any individual who had reached their 79th birthday on that specific date was eligible to receive the vaccine within the subsequent year. This phased approach meant that those who were 78 on September 1, 2013, would become eligible the following year, and so forth. Crucially, individuals who were 80 years or older on September 1, 2013, were permanently ineligible for the vaccine under this policy.
Because eligibility was determined solely by age relative to a fixed cut-off date, the distinction between being just under or just over the age threshold had a profound impact on who could access the vaccine. This created a scenario where researchers could effectively compare individuals who turned 80 shortly before September 1, 2013, with those who reached the same age milestone shortly after. This comparison allowed for an examination of how vaccine eligibility, and subsequent vaccination, influenced long-term health outcomes.
Dr. Geldsetzer highlighted the exceptional utility of this situation: "According to Geldsetzer, the detailed health records available in Wales made these circumstances about as close as possible to a randomized controlled trial without actually running one."
Comparing Near-Identical Groups for Unbiased Insights
To capitalize on this fortuitous setup, the research team meticulously analyzed the health records of over 280,000 older adults, aged between 71 and 88, who had no prior diagnosis of dementia at the commencement of the vaccination program. Their analysis then focused intently on individuals whose birthdays placed them on either side of the eligibility line. This involved a direct comparison between those who turned 80 in the week preceding September 1, 2013, and those who reached the same age in the week following this critical date.
"We know that if you take a thousand people at random born in one week and a thousand people at random, born a week later, there shouldn’t be anything different about them on average," Dr. Geldsetzer explained. "They are similar to each other apart from this tiny difference in age."
The researchers reasoned that the desire to receive the shingles vaccine would be roughly equivalent across both groups. The pivotal distinction, however, was that only the slightly younger cohort, those not yet 80 on September 1, 2013, were permitted to receive it according to the national policy.
"What makes the study so powerful is that it’s essentially like a randomized trial with a control group — those a little bit too old to be eligible for the vaccine — and an intervention group — those just young enough to be eligible," Dr. Geldsetzer elaborated.
Quantifying Protection Against Shingles and Dementia
The research team then meticulously tracked the health trajectories of these individuals for the subsequent seven years, comparing outcomes between those who were eligible for, and subsequently received, the vaccine and their ineligible peers. By integrating this information with actual vaccination rates, they were able to estimate the precise effect of receiving the shingles shot. The data indicated that approximately half of the eligible individuals did indeed get vaccinated, while virtually none of those deemed ineligible received the vaccine.
As anticipated, the vaccine demonstrated a significant impact on shingles rates, reducing its incidence by approximately 37% among those vaccinated during the seven-year follow-up period. This figure aligns with established data from clinical trials for the live-attenuated vaccine, although its effectiveness is known to diminish over time.
By 2020, when the study participants were nearing their late eighties, approximately one in eight individuals had developed dementia. However, within this cohort, those who had received the shingles vaccine exhibited a 20% lower likelihood of receiving a dementia diagnosis when compared to those who remained unvaccinated.
"It was a really striking finding," Dr. Geldsetzer stated. "This huge protective signal was there, any which way you looked at the data."
Rigorous Analysis to Rule Out Alternative Explanations
The researchers undertook a comprehensive effort to identify and eliminate any other potential factors that might account for the observed disparity in dementia rates. Their analysis revealed that the two groups—eligible and ineligible for the vaccine—were remarkably similar across a wide spectrum of measurable characteristics. Educational attainment was consistent between the groups. Individuals eligible for the shingles vaccine were not more likely to receive other vaccinations or preventive medical therapies, nor were they less prone to common chronic illnesses such as diabetes, heart disease, or cancer.
The sole significant difference identified between the groups was the demonstrably lower incidence of dementia diagnoses among those who had access to and received the shingles vaccine.
"Because of the unique way in which the vaccine was rolled out, bias in the analysis is much less likely than would usually be the case," Dr. Geldsetzer asserted.
Despite this robust initial finding, the team subjected their data to a battery of alternative analytical approaches. These included examining different age windows and focusing exclusively on mortality data where dementia was listed as a cause of death. Regardless of how the information was dissected, the consistent relationship between shingles vaccination and a reduced risk of dementia persisted.
"The signal in our data was so strong, so clear and so persistent," he emphasized.
Broader Benefits: From Early Decline to Advanced Dementia
The research team then broadened their inquiry to ascertain whether the vaccine’s apparent protective effects were confined to preventing the onset of dementia or if they extended to individuals already exhibiting early signs of cognitive decline. Leveraging the same natural experiment framework, they examined a wider range of health outcomes, encompassing mild cognitive impairment through to advanced stages of dementia.
Many diagnoses of dementia are preceded by a period of mild cognitive impairment (MCI), characterized by subtle deficits in memory and cognitive functions that do not, however, impede independent living, as explained by Dr. Geldsetzer. The study observed that individuals who had received the shingles vaccine were less likely to receive an MCI diagnosis during a nine-year follow-up period compared to their unvaccinated counterparts.
Furthermore, the researchers investigated the outcomes for individuals who had already been diagnosed with dementia at the commencement of the Welsh vaccination program. In this specific group, the findings were particularly striking. Those with existing dementia who received the shingles vaccine were significantly less likely to die from dementia within the subsequent nine years, as indicated on their death certificates, compared to those who did not receive the vaccine. This suggests a potential slowing of disease progression in the vaccinated group.
Across the entire cohort of 7,049 Welsh seniors who had dementia at the program’s start, nearly half ultimately died from the disease during the follow-up period. However, among those with dementia who had received the shingles vaccine, only approximately 30% died from the condition.
"The most exciting part is that this really suggests the shingles vaccine doesn’t have only preventive, delaying benefits for dementia, but also therapeutic potential for those who already have dementia," Dr. Geldsetzer remarked.
Sex-Specific Effects and Unanswered Questions
An intriguing pattern emerged when the researchers analyzed the outcomes by sex. The protective effect of the shingles vaccine against dementia appeared to be substantially more pronounced in women than in men. Dr. Geldsetzer posited that this discrepancy might reflect underlying biological differences in immune responses between the sexes or variations in how dementia manifests in men and women. It is known that women, on average, tend to mount stronger antibody responses following vaccination, and shingles itself occurs more frequently in women.
At present, the precise biological mechanisms through which the vaccine confers protection remain a subject of ongoing investigation. Scientists are exploring whether the benefit stems from a broad stimulation of the immune system, a reduction in the frequency of VZV reactivation, or an entirely different pathway.
Furthermore, it is currently unknown whether the newer generation of shingles vaccines, which employ recombinant protein technology and offer enhanced protection against shingles itself, would yield similar or even greater benefits in terms of dementia risk reduction.
Global Replication and the Push for Randomized Trials
Dr. Geldsetzer expressed hope that these findings will stimulate increased investment in this critical area of research. "At least investing a subset of our resources into investigating these pathways could lead to breakthroughs in terms of treatment and prevention," he urged.
Over the past two years, his team has conducted similar analyses of health records from other countries, including England, Australia, New Zealand, and Canada, where comparable shingles vaccine rollout programs were implemented. The results from these diverse datasets have consistently mirrored those observed in Wales. "We just keep seeing this strong protective signal for dementia in dataset after dataset," he confirmed.
The next crucial step, as envisioned by Dr. Geldsetzer, is the initiation of a large-scale randomized controlled trial. Such a trial would provide the most rigorous evidence to definitively establish whether the vaccine causally reduces dementia risk. In this proposed study, participants would be randomly assigned to receive either the live-attenuated shingles vaccine or a placebo injection.
"It would be a very simple, pragmatic trial because we have a one-off intervention that we know is safe," he stated.
Dr. Geldsetzer is actively seeking philanthropic support to fund this endeavor. This is partly necessitated by the fact that the live-attenuated vaccine, for which substantial evidence has been gathered from natural experiments, is now off-patent.
He also pointed out that such a trial could yield meaningful results relatively swiftly. The Welsh data demonstrated that when dementia rates were plotted for eligible versus ineligible individuals, the two curves began to diverge noticeably after approximately eighteen months.
This pioneering research, involving contributions from a researcher at the Vienna University of Economics and Business, was supported by grants from The Phil & Penny Knight Initiative for Brain Resilience, the Stanford Center for Digital Health, the National Institute on Aging (grant R01AG084535), the National Institute of Allergy and Infectious Diseases (grant DP2AI171011), and the Biohub, San Francisco.
