By Hendra Lukman 
An unprecedented analysis of health records from Wales has provided some of the most compelling evidence to date suggesting that a vaccine, specifically the shingles vaccine, may play a significant role in protecting against dementia. The groundbreaking study, spearheaded by researchers at Stanford Medicine, examined the health trajectories of older adults and discovered that individuals who received the shingles vaccine exhibited a 20% lower likelihood of being diagnosed with dementia within the subsequent seven years compared to their unvaccinated counterparts.
A "Natural Experiment" Unveils a Potential Dementia Defense
Published on April 2nd in the prestigious journal Nature, these findings lend substantial support to an emerging hypothesis within the scientific community: that certain viruses with a propensity to affect the nervous system could elevate the risk of developing dementia. Should these initial results be corroborated by further investigation, they could point towards a readily available and practical strategy for dementia prevention, a prospect that has long eluded researchers focused on other avenues, such as the intricate pathways of protein aggregation in the brain.
The implications of this research extend beyond mere prevention. A secondary analysis from the same research team, detailed in Cell on December 2nd, suggests that the shingles vaccine might also offer therapeutic benefits for individuals already living with dementia, potentially slowing the progression of the disease. This dual-action potential marks a significant development in the ongoing battle against neurodegenerative disorders.
Understanding the Shingles Virus and Its Lifelong Presence
Shingles, a painful and debilitating viral disease characterized by a blistering rash, is caused by the varicella-zoster virus (VZV). This is the same virus responsible for chickenpox, a common childhood illness. Upon initial infection with chickenpox, the VZV does not entirely leave the body. Instead, it lies dormant within the nerve cells, remaining a lifelong resident. In later years, particularly in older adults or individuals with compromised immune systems, this latent virus can reactivate, leading to the development of shingles.
The Dementia Crisis and the Shifting Research Paradigm
Globally, dementia currently affects over 55 million individuals, with approximately 10 million new cases diagnosed annually. For decades, the primary focus of dementia research has been on the accumulation of abnormal proteins in the brain, specifically amyloid plaques and tau tangles, which are hallmarks of Alzheimer’s disease, the most prevalent form of dementia. However, despite extensive efforts, these approaches have yet to yield effective methods for preventing or halting the disease’s advance. This lack of progress has prompted some scientists to explore alternative contributing factors, including chronic viral infections that may inflict cumulative damage on the brain over time.
Previous observational studies, which relied on the analysis of large health datasets, had hinted at a potential association between shingles vaccination and a reduced incidence of dementia. However, these studies were hampered by a significant limitation: selection bias. Individuals who opt for vaccination are often characterized by a more health-conscious lifestyle, engaging in behaviors such as healthier eating, increased physical activity, and more regular engagement with healthcare providers. These lifestyle factors, known to influence dementia risk, are notoriously difficult to quantify and are often not captured in medical databases, making it challenging to isolate the vaccine’s true effect.
Dr. Pascal Geldsetzer, MD, PhD, an assistant professor of medicine and 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 Unique Opportunity: The Welsh Vaccination Rollout as a Natural Experiment
Approximately two years ago, Dr. Geldsetzer identified a unique circumstance arising from the way Wales implemented its shingles vaccination program. This specific rollout strategy functioned as what researchers term a "natural experiment," effectively mitigating much of the bias that plagued earlier investigations. At the time of the program’s inception, Wales utilized a live-attenuated (weakened) form of the VZV vaccine.
The national program commenced on September 1, 2013. The policy dictated that any individual who reached the age of 79 on that specific date was eligible to receive the vaccine within the following year. Those who turned 78 would become eligible the subsequent year for a one-year window, and so forth. Crucially, individuals aged 80 or older on September 1, 2013, were deemed ineligible for the vaccine under this program, meaning they would never have the opportunity to receive it.
This age-based eligibility criterion, dependent solely on one’s age relative to a precise cut-off date, created a stark contrast in vaccine access between individuals who were just under and just over the eligibility threshold. This scenario allowed researchers to meticulously compare individuals who turned 80 shortly before September 1, 2013, with those who reached the same age shortly after, thereby assessing the long-term outcomes associated with vaccine eligibility.
Dr. Geldsetzer highlighted the significance of this situation: "Because eligibility depended only on age at a specific cut-off date, the difference between being just under or just over the age threshold had a major impact on who could get the shot." He further elaborated that the detailed and comprehensive 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 Cohorts: The Power of Age Proximity
To leverage this exceptional research opportunity, the Stanford team meticulously analyzed the health records of over 280,000 older adults, aged between 71 and 88, who did not have a dementia diagnosis at the program’s outset. Their analysis then zeroed in on individuals whose birthdays placed them precisely on either side of the eligibility line. This involved comparing those who turned 80 in the week preceding September 1, 2013, with those who reached the same age in the week following this pivotal 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 posited that a comparable proportion of individuals in both groups would have desired the shingles vaccine. The critical differentiator, however, was that only the slightly younger cohort, those not yet 80 on September 1, 2013, were permitted to receive it according to the established rules.
"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 emphasized.
Quantifying Protection: Shingles and Dementia Risk Reduction
The research team then meticulously tracked the health outcomes of these carefully selected individuals for the subsequent seven years, directly comparing those who were eligible for the vaccine with those who were not, while accounting for similar ages. By integrating this data with actual vaccination rates, they were able to estimate the precise impact of receiving the shingles shot. The findings indicated that approximately half of the eligible individuals ultimately received the vaccine, while a negligible proportion of those deemed ineligible obtained it.
As anticipated, the vaccine demonstrated a significant reduction in shingles incidence, lowering the rate by approximately 37% among vaccinated individuals over the seven-year follow-up period. This result aligns with efficacy data from clinical trials for the live-attenuated vaccine, although its effectiveness is known to wane over time.
By the year 2020, when the study participants were around 86 and 87 years old, the data revealed that one in eight individuals had developed dementia. However, within the subgroup that received the shingles vaccine, the likelihood of receiving a dementia diagnosis was found to be a notable 20% lower compared to those who remained unvaccinated.
"It was a really striking finding," Dr. Geldsetzer remarked. "This huge protective signal was there, any which way you looked at the data."
Rigorous Analysis: Ruling Out Confounding Factors
The researchers undertook a comprehensive effort to identify and rule out any alternative explanations for the observed disparity in dementia rates between the vaccinated and unvaccinated groups. They meticulously examined a wide array of measurable characteristics and found the two cohorts to be remarkably similar. Educational attainment was identical for both eligible and ineligible individuals. Those who qualified for the shingles vaccine were not statistically more likely to receive other vaccinations or preventive medical treatments, nor were they less likely to suffer from common chronic illnesses such as diabetes, heart disease, or cancer.
The only significant and consistent difference identified between the groups was the 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 stated, underscoring the robustness of their findings.
Despite the strength of their initial results, the research team subjected their data to a variety of alternative analytical approaches. This included examining different age windows and focusing solely on mortality data where dementia was listed as a cause of death. Regardless of how the information was parsed, the association between shingles vaccination and a reduced risk of dementia remained consistently strong and significant.
"The signal in our data was so strong, so clear and so persistent," he reiterated.
Beyond Prevention: Therapeutic Potential in Early Decline and Advanced Dementia
The researchers further explored whether the observed benefits of the shingles vaccine were confined to preventing the onset of dementia or if they also extended to individuals who were already exhibiting early signs of cognitive impairment. Employing the same natural experiment framework, they broadened their investigation to encompass a wider spectrum of outcomes, ranging from subtle cognitive changes to advanced stages of dementia.
A significant portion of dementia cases are often preceded by a period of mild cognitive impairment (MCI), characterized by deficits in memory and cognitive functions that, while noticeable, do not yet impede independent living. Dr. Geldsetzer noted that the team 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.
Their investigation also delved into the outcomes of individuals who had already been diagnosed with dementia at the commencement of the Welsh vaccination program. In this specific group, the findings were particularly compelling. Individuals with dementia who received the shingles vaccine demonstrated a significantly lower likelihood of dying from dementia within the subsequent nine years, as indicated on their death certificates, compared to those who did not receive the vaccine. This suggests that the disease may have progressed at a slower pace in the vaccinated individuals.
In total, nearly half of the 7,049 Welsh seniors who had dementia when the program began ultimately died from the condition during the follow-up period. However, among those with dementia who received the shingles vaccine, only approximately 30% died from the disease.
"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 expressed with evident enthusiasm.
Sex-Specific Effects and Unanswered Questions
An intriguing pattern emerged when the researchers analyzed outcomes based on 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 disparity could be attributed to biological differences in immune responses or variations in how dementia manifests in men and women. On average, women tend to mount stronger antibody responses following vaccination, and shingles itself occurs more frequently in women than in men.
At present, the precise biological mechanisms through which the vaccine might confer protection remain an open question. It is unclear whether the vaccine operates by broadly stimulating the immune system, by reducing the frequency of varicella-zoster virus reactivation, or through an entirely different pathway.
Furthermore, it is yet to be determined whether newer shingles vaccines, which utilize specific viral proteins and offer enhanced protection against shingles, would exhibit a similar or even more potent effect on dementia risk.
Global Corroboration and the Pursuit of a Definitive Trial
Dr. Geldsetzer expressed optimism 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 expanded their analysis to include health records from other countries, such as England, Australia, New Zealand, and Canada, which have implemented similar shingles vaccine rollout programs. The results from these diverse datasets have consistently mirrored the observations made in Wales. "We just keep seeing this strong protective signal for dementia in dataset after dataset," he reported.
The ultimate goal for Dr. Geldsetzer and his team is to conduct a large-scale randomized controlled trial (RCT). Such a trial would provide the most rigorous scientific evidence to definitively establish whether the vaccine indeed causes the observed reduction in dementia incidence. In an RCT, participants would be randomly assigned to receive either the live-attenuated shingles vaccine or a placebo injection, thereby minimizing bias and allowing for definitive causal inferences.
"It would be a very simple, pragmatic trial because we have a one-off intervention that we know is safe," Dr. Geldsetzer noted.
He is actively seeking philanthropic support to fund this crucial endeavor, particularly given that the live-attenuated vaccine, for which he has gathered substantial evidence from natural experiments, is now off-patent.
Dr. Geldsetzer also pointed out that such a trial could yield meaningful results relatively swiftly. The Welsh data indicated that the divergence in dementia rates between eligible and ineligible individuals began to become apparent approximately eighteen months after the program’s commencement.
This groundbreaking research was further supported by contributions from a researcher at the Vienna University of Economics and Business. The study received funding 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.
