"Beyond direct disease prevention, vaccinations for older adults are increasingly revealing ‘indirect benefits’—positive health outcomes that extend far beyond their intended targets, including a potential reduction in dementia and cardiovascular events."
This groundbreaking insight highlights a rapidly evolving understanding of vaccine efficacy. While the primary purpose of vaccinations has always been to shield individuals from specific infectious diseases, emerging research indicates that these medical interventions may offer a broader spectrum of health advantages. These "indirect benefits" are prompting a re-evaluation of vaccination strategies, particularly for the aging population, suggesting that vaccines are powerful tools for promoting overall well-being and mitigating age-related cognitive and physical decline.
The landscape of adult vaccination is undergoing a significant transformation, revealing that immunizations offer a surprising array of benefits that extend far beyond their primary targets. While the direct protection against diseases like shingles, respiratory syncytial virus (RSV), and influenza remains paramount, a growing body of evidence points to profound "indirect benefits." These advantages, supported by accumulating research over the past decade, suggest that vaccines are not merely shields against specific infections but are increasingly recognized as crucial tools for promoting healthier aging, reducing the risk of chronic conditions, and even potentially warding off cognitive decline.
For years, the primary impetus for vaccination has been clear and compelling. Two doses of the shingles vaccine, for instance, provide an impressive approximately 90% protection against this painful, blistering infection caused by the varicella-zoster virus. Shingles can lead to persistent nerve pain, known as postherpetic neuralgia, and other severe long-term complications. This disease affects about a third of Americans over their lifetime, making vaccination a critical preventative measure. Similarly, for older adults, the vaccine against RSV significantly lowers the risk of hospitalization due to this common respiratory infection. Studies indicate that within the year of vaccination, hospitalization risk can decrease by nearly 70%, with a sustained reduction of around 60% in the two years following. The annual flu vaccine, while varying in effectiveness based on the accuracy of predicting circulating strains, reliably reduces the severity of illness, even if it doesn’t always prevent infection.
However, the conversation around vaccines for older adults is expanding to encompass these remarkable indirect benefits. These effects, often referred to as "collateral benefits" in medical parlance, represent positive outcomes that transcend the prevention of the specific disease for which a vaccine was designed. As Dr. William Schaffner, an infectious disease specialist at Vanderbilt University Medical Center, notes, research in this area has "accumulated and accelerated over the last 10 years." Some of these protective effects have been observed for decades, while others are emerging from more recent studies, with their full implications still being elucidated. The RSV vaccine, for example, only became widely available in 2023, making its long-term indirect benefits a subject of ongoing investigation.
Despite the growing evidence, a significant portion of older adults remain undervaccinated. This is particularly concerning given that their immune systems naturally weaken with age, and the prevalence of chronic health conditions further elevates their risk of contracting infectious diseases. Data from the Centers for Disease Control and Prevention (CDC) in mid-December revealed that approximately 37% of older adults had not yet received the annual flu vaccine. Only 42% had ever received the RSV vaccine, and fewer than a third had received the most recent COVID-19 vaccine. Similarly, uptake of the pneumococcal vaccine, recommended for adults aged 50 and older, remains surprisingly low. An analysis in the American Journal of Preventive Medicine estimated that between 2022 and 2024, only 12% of individuals aged 67-74 and a mere 8% of those over 75 had received the updated vaccine following recommendation changes.
The most robust evidence for indirect benefits, spanning approximately 25 years, points to a reduction in cardiovascular risk following influenza vaccination. Healthy older adults who receive the flu shot exhibit a significantly lower risk of hospitalization due to heart failure, as well as pneumonia and other respiratory infections. Furthermore, influenza vaccination has been linked to a reduced risk of heart attack and stroke. It’s important to note that many of these studies predated the availability of more potent flu vaccines currently recommended for older adults, suggesting that the protective effects might be even more pronounced with contemporary formulations.
This raises a pertinent question: could the RSV vaccine, which targets another serious respiratory illness, offer similar cardiovascular advantages? A large-scale study conducted in Denmark among older adults found a nearly 10% reduction in cardiorespiratory hospitalizations (involving both the heart and lungs) among vaccinated individuals compared to a control group—a statistically significant finding. However, the reduction in hospitalizations specifically for cardiovascular diseases and strokes was not statistically significant. Dr. Helen Chu, an infectious disease specialist at the University of Washington and co-author of an editorial accompanying the study in JAMA, suggests this might be due to a short follow-up period or inadequate diagnostic testing. "I don’t think RSV behaves very differently from influenza," Chu commented, expressing optimism that further data on RSV will reveal similar, potentially even greater, protective effects.
Vaccination against COVID-19, another dangerous respiratory illness, has also been associated with a reduced risk of developing "long COVID," a condition with debilitating physical and mental health consequences.
Perhaps the most provocative findings emerge from research on the shingles vaccine. Last year, headlines were made when studies demonstrated an association between shingles vaccination and lower rates of dementia. This association was observed even with an older, less effective version of the vaccine, which has since been superseded by Shingrix, approved in 2017.
The majority of studies exploring indirect benefits are observational in nature. This is due to ethical considerations; researchers cannot ethically withhold a safe and effective vaccine from a control group that might otherwise contract the targeted disease. Consequently, results can be influenced by "healthy volunteer bias," where individuals who choose to be vaccinated may also engage in other healthy behaviors that differentiate them from those who do not. While researchers strive to adjust for factors like age, sex, health status, and education level, "we can only state that there is a strong association between the vaccine and the reduction in dementia, but not a causal relationship," explained Dr. Stefania Maggi, a geriatrician and senior researcher at the National Research Council Neuroscience Institute in Padua, Italy. Maggi is the lead author of a recent meta-analysis published in the journal Age and Ageing that found a reduced risk of dementia following vaccination against various diseases.
To address the limitations of observational studies, researchers at Stanford utilized a natural experiment in Wales. In 2013, the first shingles vaccine, Zostavax, was offered to individuals aged 70-79, with those 80 and older excluded. Over a seven-year period, dementia rates among those eligible for the vaccine—even those who did not ultimately receive it—decreased by 20% compared to the control group who missed eligibility by mere days. "There’s no reason to think people born a week earlier were different from those born a few days later," Maggi stated, providing compelling evidence for a causal link. Additional studies in Australia and the United States have also found that shingles vaccination reduces the likelihood of developing dementia.
In fact, Maggi’s review of studies revealed that several childhood and adult vaccines appear to confer similar indirect benefits. "We now know that many infections are associated with the development of dementia, whether it’s Alzheimer’s or vascular dementia," she explained. Across 21 studies involving over 104 million participants in Europe, Asia, and North America, shingles vaccination was linked to a 24% reduction in dementia risk. The influenza vaccine showed a 13% reduction, and the pneumococcal vaccine was associated with a 36% lower risk of Alzheimer’s disease.
The Tdap vaccine, protecting against tetanus, diphtheria, and pertussis (whooping cough), was associated with a one-third reduction in dementia risk. Adults are recommended to receive this vaccine every 10 years, and many choose to get it when a grandchild is born, as newborns cannot receive their full vaccination series in their earliest months. Researchers are also exploring whether the shingles vaccine can reduce the risk of heart attacks and strokes, and if COVID-19 vaccination can improve survival rates for cancer patients.
What underlies these additional benefits of vaccines? Most hypotheses center on the inflammatory response triggered when the immune system combats an infection. "Damage is done to the environment surrounding the body’s cells, and it takes time to return to normal," explained Dr. Chu. The effects of inflammation can linger long after the initial illness, potentially facilitating the development of other infections or contributing to heart attacks and strokes when blood clots form in narrowed vessels. "If you prevent the infection, you also prevent that downstream damage," Chu added.
Hospitalization itself, where older patients may experience loss of strength, mobility, or develop delirium, is a risk factor for dementia and other health issues. Therefore, vaccines that help prevent hospitalization could potentially delay or even prevent cognitive deterioration.
Concerns have been raised about the current national vaccination policy, with some health officials from the Trump administration having questioned childhood vaccines more than adult ones. This open opposition may have inadvertently contributed to a reluctance among many older adults to get vaccinated. Consequently, they risk not only missing out on the burgeoning indirect benefits but also remaining vulnerable to preventable or manageable diseases.
"The current national policy on vaccination is, at best, ambiguous, and in some aspects appears anti-vaccine," stated Schaffner, a former member of the CDC’s Advisory Committee on Immunization Practices. "All of us in public health are really very concerned." This sentiment underscores the urgent need for clear, evidence-based communication to encourage widespread vaccination and harness the full spectrum of benefits that these vital medical interventions offer.