Routine immunizations against common viral and bacterial infections might offer an unexpected benefit by protecting the brain from cognitive decline in old age. A growing body of scientific literature suggests that standard vaccinations are associated with a reduced risk of developing dementia and Alzheimer’s disease later in life.
Dementia is a broad term for a severe decline in mental ability that interferes with daily life, and Alzheimer’s disease is its most common form. This progressive condition gradually destroys memory and thinking skills as brain cells are damaged and eventually die. The exact biological triggers for this brain damage remain a topic of intense scientific investigation.
Medical professionals have observed a link between severe infectious diseases and cognitive decline for quite some time. Severe infections cause widespread inflammation throughout the entire body. This persistent state of heightened alert can compromise the blood-brain barrier, which is a tight layer of cells that normally protects the brain from toxins and pathogens circulating in the bloodstream.
When this protective barrier breaks down, harmful proteins and inflammatory immune cells can enter the delicate brain tissue. This infiltration promotes a state of chronic immune activation inside the brain, known as neuroinflammation. Such an environment is known to play a major role in the destruction of brain cells seen in dementia patients.
Because of this biological pathway, scientists have been investigating whether preventing infections might also protect the brain. Vaccines are designed to stop or lessen the severity of infections. By doing so, they might reduce the overall inflammatory burden on the body and help maintain the integrity of the blood-brain barrier.
Scientists are also exploring the idea that vaccines, particularly live-attenuated vaccines, might offer broader health benefits than just preventing their specific target diseases. Live vaccines contain a weakened, harmless form of a virus. These formulations stimulate a very strong response from the body’s innate immune system.
This general immune boost might train the body to better regulate inflammation as we age. This concept is known in the medical field as trained immunity. A stronger, more refined immune system could potentially protect against various age-related chronic diseases, including conditions that degrade cognitive health.
To investigate these theories, a research team analyzed a massive database of health insurance records from a company called Optum. Their study was published on September 12, 2023, in the Journal of Alzheimer’s Disease. The researchers looked at anonymized medical records spanning from 2009 to 2019, focusing on adults aged 65 and older.
The scientists excluded anyone who already had a diagnosis of dementia or mild memory problems before the study officially began. They then tracked who received routine vaccinations for tetanus and diphtheria, shingles, or pneumonia. They compared the health outcomes of these vaccinated individuals against unvaccinated individuals over an eight-year follow-up period.
To ensure a fair comparison, the researchers used a statistical technique called propensity score matching. This method balances out differences between people who choose to get vaccinated and those who do not. The researchers matched individuals based on age, sex, geographic region, pre-existing health conditions, and even the number of routine doctor visits.
The researchers found that vaccination against tetanus and diphtheria was associated with a 30 percent lower risk of developing Alzheimer’s disease. Receiving a shingles vaccine was linked to a 25 percent reduction in Alzheimer’s risk. In a similar trend, pneumococcal vaccination was associated with a 27 percent lower risk of the disease.
To ensure their findings were not just the result of health-conscious people getting more vaccines, the researchers ran a sensitivity analysis. They looked only at patients who consistently took statin medications for cholesterol, which is a strong indicator of proactive health behavior. Even within this specific health-conscious group, the protective associations between vaccinations and a reduced risk of Alzheimer’s disease held steady.
A later study provided even stronger evidence for this protective effect by taking advantage of a unique natural experiment in Wales. This research was published on April 2, 2025, in the journal Nature. The scientists looked at the rollout of the live-attenuated herpes zoster vaccine, which is designed to prevent shingles.
Shingles is a painful skin rash caused by the varicella-zoster virus, the exact same virus responsible for chickenpox. After a childhood chickenpox infection clears, the virus retreats into the nervous system and goes completely dormant. As people age and their immune defenses naturally wane, the virus can wake up and cause a shingles outbreak.
In Wales, eligibility for the government-funded shingles vaccine was determined by a strict date-of-birth cutoff. Individuals born before September 2, 1933, were ineligible and remained ineligible for life. On the other hand, adults born on or exactly after September 2, 1933, were eligible to receive the vaccine for at least one year.
This arbitrary cutoff meant that the vaccination rate jumped from a mere 0.01 percent among patients who were just one week too old, up to 47.2 percent among those who were just one week younger. Individuals born just days apart are highly unlikely to differ systematically in terms of genetics, wealth, or general health. The only major difference between these two groups was their probability of receiving the shingles vaccine.
The researchers used an analytical approach called a regression discontinuity design to analyze electronic health records from 282,541 adults. This method measures the abrupt change in health outcomes exactly at the birthdate cutoff. Over a seven-year follow-up period, the researchers found that receiving the shingles vaccine reduced the probability of a new dementia diagnosis by 3.5 percentage points.
On a relative scale, this translated to a 20 percent reduction in new dementia diagnoses for the vaccinated group. The protective effect was found to be even stronger among women than men. The researchers confirmed these findings using a second dataset of death certificates from England and Wales, noting a similar reduction in deaths where dementia was listed as the primary cause.
Other routine vaccines, such as the seasonal flu shot, have also shown promise in preserving cognitive health. A scientific commentary published on January 16, 2026, in Aging Clinical and Experimental Research synthesized data from multiple large-scale epidemiological studies. The authors proposed that the annual influenza vaccine provides neurological protection that extends well beyond simply preventing a respiratory illness.
The authors highlighted that an influenza infection is a systemic illness that can cause severe complications throughout the human body. Research indicates that the risk of acute heart attacks and strokes can be six times greater in the first week after a severe flu infection. Because brain health is heavily dependent on a healthy vascular system, preventing these blood-flow disruptions helps preserve cognitive reserves.
The perspective article cited a massive meta-analysis of over two million adults, which found that individuals who received flu shots had a 31 percent lower risk of developing dementia. Another cited study utilizing data from the United Kingdom Biobank found a dose-response relationship. This means that the protective signal was strongest among participants who received multiple flu vaccine doses across different years, rather than just a single shot.
The biological changes caused by these vaccines happen deep within the body’s cells. A study published on January 20, 2026, in The Journals of Gerontology, Series A investigated whether the shingles vaccine actually slows the rate of biological aging. While chronological age measures the number of birthdays a person has had, biological age measures the actual wear and tear on tissues and organs.
The researchers analyzed blood samples from nearly 4,000 adults over the age of 70, using data from the national Health and Retirement Study. They looked at specific molecular markers, known as epigenetic clocks, which estimate how genes are regulated and expressed as cells age. They also measured markers of systemic inflammation across the body.
The results showed that individuals who had received the shingles vaccine displayed significantly lower levels of C-reactive protein, a primary marker for bodily inflammation. The vaccinated participants also possessed younger cellular profiles according to their epigenetic clocks. When the researchers combined multiple measures into a single composite score, the vaccinated group demonstrated a healthier overall biological profile.
Surprisingly, the researchers found no association between the shingles vaccination and specific blood biomarkers for neurodegeneration, such as phosphorylated tau proteins. The levels of brain injury proteins were essentially the same in both the vaccinated and unvaccinated groups. This suggests that blood-based biomarkers might not be sensitive enough to capture the exact type of neuroprotection the vaccine offers, or the protective effects on the brain take longer to manifest than the study allowed.
The underlying danger of severe infections was further documented in a nationwide registry study published on March 24, 2026, in PLOS Medicine. Researchers analyzed the health records of the Finnish population to see if severe infections independently elevate dementia risk. The dataset included 62,555 individuals aged 65 or older who received a late-onset dementia diagnosis, matched against 312,772 control individuals without dementia.
Older patients typically suffer from a variety of overlapping physical and mental ailments, making it difficult to isolate the exact cause of cognitive decline. The researchers reviewed up to 21 years of prior medical records for each participant to map how various illnesses connected to one another. They found that severe, hospital-treated infections consistently preceded dementia diagnoses.
Even after adjusting their mathematical models to account for 27 other non-infectious conditions, the link remained robust. An individual hospitalized for a severe urinary tract infection or an unspecified bacterial infection faced a 19 percent relative increase in the rate of eventually developing dementia. The researchers suggest that a massive inflammatory event might speed up the deterioration in a brain already poised to develop cognitive issues.
A subsequent study from South Korea provided additional evidence regarding the live-attenuated shingles vaccine. Published in April 2026 in Alzheimer’s & Dementia, this research analyzed data from over two and a half million adults aged 50 and older. The authors gathered medical claims, prescription records, and national health examination results from the country’s universal health insurance system.
The researchers focused entirely on the live shingles vaccine, which is administered as a single dose in South Korea. They tracked new medical diagnoses that occurred at least thirty days after the vaccination date. To ensure an exact comparison, the researchers matched vaccinated and unvaccinated groups based on medical factors like body weight, blood pressure, fasting blood sugar, and preexisting conditions like high cholesterol.
“We were initially interested in the possibility that live zoster vaccination may have broader health benefits beyond preventing shingles,” Dong Keon Yon, a professor of pediatrics and digital health at Kyung Hee University College of Medicine, previously told PsyPost. “Some previous research, including our own work, suggested that the vaccine might be associated with lower risks of several aging-related outcomes, such as cardiovascular disease and allergic or immune-related conditions.”
The final matched analysis included just over one million people. The researchers tracked the health outcomes of these individuals for up to 12 years. They found that people who received the live shingles vaccine had a 12 percent lower risk of developing memory disorders and a 25 percent lower risk of developing Alzheimer’s disease.
“One finding that stood out to us was the consistency of the association across cognitive outcomes,” Yon previously told PsyPost. “The vaccinated group had lower risks of both memory disorders and Alzheimer’s disease, suggesting that the observed association was not limited to a single cognitive outcome.”
Over a ten-year period, the vaccinated group lived without memory disorders for an average of about 15 and a half extra days compared to the unvaccinated group. This specific timeframe suggests that the vaccine tends to slightly delay the onset of cognitive decline rather than completely stopping it. The strongest reduction in risk occurred during the first two to four years after the vaccination, slowly fading out after six years.
“The average person should take away that zoster vaccination may have benefits beyond preventing shingles,” Yon previously told PsyPost. “In our study, older adults who received the live zoster vaccine had a lower risk of developing memory disorders and Alzheimer’s disease, suggesting that vaccination may be linked to broader aspects of healthy aging.”
“At the same time, this does not mean that the zoster vaccine should be viewed as a dementia-prevention treatment,” Yon continued. “The practical message is that staying up to date with recommended vaccinations in older adulthood may be an important part of protecting long-term health, and cognitive health may be one area where these benefits deserve further study.”
“We think one important message is that vaccines in older adulthood should be viewed as a key part of preventive health. At the same time, cognitive health is influenced by many factors, including vascular health, lifestyle, chronic disease management, and social factors.”
“As with any large real-world data study, the findings should be interpreted in the context of the study design,” Yon said. “Our long-term goal is to better understand how adult vaccination may contribute to healthy aging beyond the prevention of a single infectious disease.”
The most recent study on this topic, published on June 16, 2026, in the Annals of Internal Medicine, shifted focus to the newer, recombinant version of the shingles vaccine. Recombinant vaccines are made by synthetically producing specific pieces of a virus to trigger a strong immune response, rather than using a live, weakened virus. This newer version, known by the brand name Shingrix, is highly effective at preventing shingles in older adults.
Researchers focused on older adults admitted to skilled-nursing facilities across the United States. These inpatient medical centers provide short-term rehabilitation and long-term care for frail populations. The scientists utilized a target trial emulation, an analytical approach that mimics the design of a randomized controlled experiment using existing observational data.
The sample included 509,926 participants with an average age of 79 years. The researchers tracked the patients using Medicare claims from January 2017 to December 2022. They looked for new dementia diagnoses using medical billing codes from hospital stays, physician claims, and pharmacy records.
“We examined the link between vaccination with Shingrix because shingles increases the risk of stroke and potentially just general inflammation in the brain,” Kaley Hayes, an associate professor at Brown University, previously told PsyPost. “There is a hypothesis that reducing activity of the virus that causes shingles (called herpes zoster), might therefore help to prevent brain inflammation that can damage brain health long-term.”
“Prior studies in different populations that examined the older vaccine, Zostavax, did find a signal for dementia prevention,” Hayes explained. “We wanted to use large, real-world data and a rigorous study design to find out if that signal exists for older adults in the US vaccinated with the newer, more effective vaccine.”
The researchers found that the vaccinated group had an 18.8 percent risk of developing dementia over the four-year follow-up period. In comparison, the unvaccinated group faced a 24.6 percent risk. This represented a 24 percent lower relative risk of being diagnosed with dementia for those who received the newer recombinant vaccine.
“Our study identified that as many as 1 in 17 cases of dementia might be prevented through shingles vaccination, though trials are needed to confirm these findings,” Hayes previously told PsyPost. “The main takeaway is that the shingles vaccine is highly effective at preventing shingles, which is painful and can cause long-term health issues. And now there is evidence that something to prevent this physical ailment may help to keep our brain healthy, too.”
Interpreting these findings requires an understanding of the limitations inherent to observational research. The vast majority of the data in these studies comes from electronic health records and insurance claims, which can identify associations but cannot definitively prove a direct cause-and-effect relationship. Insurance claims can sometimes contain coding errors or miss mild cases of cognitive decline entirely if patients delay seeking medical care.
One major complication in vaccine research is what scientists call the healthy vaccinee bias. This concept suggests that people who choose to get vaccinated might also engage in other healthy behaviors, such as eating a better diet or exercising more frequently. They might generally be more proactive about their health or have better access to medical resources than those who skip vaccines.
Researchers attempt to control for this bias using complex statistical matching and negative control analyses. For example, testing if a vaccine prevents unrelated issues like hip fractures helps scientists see if the vaccinated group is simply more cautious overall. Even with these strict adjustments, unmeasured factors like a person’s level of social engagement or the mental complexity of their daily work are often missing from national databases.
Future research will need to include actual randomized controlled trials in various clinical settings. By randomly assigning vaccines in a controlled environment, scientists can definitively rule out healthy user biases. Tracking biological markers of neuroinflammation over even longer periods will also help confirm the exact mechanisms protecting the brain.
The study, “The Impact of Routine Vaccinations on Alzheimer’s Disease Risk in Persons 65 Years and Older: A Claims-Based Cohort Study using Propensity Score Matching,” was authored by Kristofera Harris, Yaobin Ling, Avram S. Bukhbinder, Luyao Chen, Kamal N. Phelps, Gabriela Cruz, Jenna Thomas, Yejin Kim, Xiaoqian Jiang, and Paul E. Schulz.
The study, “A natural experiment on the effect of herpes zoster vaccination on dementia,” was authored by Markus Eyting, Min Xie, Felix Michalik, Simon Heß, Seunghun Chung, and Pascal Geldsetzer.
The study, “From breath to brain: influenza vaccination as a pragmatic strategy for dementia prevention,” was authored by Lorenzo Blandi and Marco Del Riccio.
The study, “Association between shingles vaccination and slower biological aging: Evidence from a U.S. population-based cohort study,” was authored by Jung Ki Kim and Eileen M. Crimmins.
The study, “The role of noninfectious comorbidities in the association between severe infections and risk of dementia in Finland: A nationwide registry study,” was authored by Pyry N. Sipilä, Kaarina Korhonen, Joni V. Lindbohm, Mika Kivimäki, and Pekka Martikainen.
The study, “Herpes zoster vaccination and cognitive disorders in older adults,” was authored by Jiyeon Oh, Kyeongmin Lee, Dongjin Yeo, Jaehyeong Cho, Tae Hyeon Kim, Jinseok Lee, Hayeon Lee, Ho Geol Woo, and Dong Keon Yon.
The study, “Dementia Risk After Recombinant Herpes Zoster Vaccination in Older Adults With a Recent Skilled-Nursing Facility Stay: A Target Trial Emulation,” was authored by Kaleen N. Hayes, Daniel A. Harris, Kevin W. McConeghy, Lexie R. Grove, Richa Joshi, Lisa Han, H. Edward Davidson, Preeti Chachlani, Thomas A. Bayer, Mriganka Singh, Yasin Abul, Frank DeVone, and Stefan Gravenstein.
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