"Vaccines are increasingly proving to be powerful tools not just for preventing specific diseases, but for promoting overall health and potentially delaying cognitive decline, offering significant ‘indirect benefits’ for older adults."
This insight highlights a growing body of scientific evidence suggesting that vaccines recommended for adults, particularly those aged 50 and older, extend their protective reach far beyond their intended targets. While the primary goal of vaccination remains to prevent illness, a deeper understanding of immunology and ongoing research reveals a cascade of positive effects, including reduced risks of cardiovascular events and even dementia. This expanded view underscores the critical importance of vaccination for healthy aging and public health.
The primary rationale for receiving vaccinations against common infectious diseases like shingles, Respiratory Syncytial Virus (RSV), and influenza is well-established and directly related to preventing serious illness. For shingles (herpes zoster), two doses of the vaccine offer a remarkable 90% protection against a painful, blistering condition that can lead to persistent nerve pain and other severe long-term complications. This viral infection, a reactivation of the varicella-zoster virus, affects approximately one-third of Americans during their lifetime, making robust prevention a significant public health priority.
Similarly, for older adults, the impact of RSV vaccination is substantial. The most compelling reason for this demographic to get vaccinated is the significant reduction in hospitalization risk. Studies indicate that vaccination can decrease the risk of RSV-related hospitalization by nearly 70% in the first year after administration and by approximately 60% in the two years following. This is particularly crucial given that RSV can cause severe respiratory illness in older individuals, leading to pneumonia and bronchitis.
The annual influenza vaccine, while variable in its year-to-year effectiveness, reliably reduces the severity of illness. This is a critical benefit, as even a less potent vaccine can significantly mitigate the risk of severe complications, hospitalization, and death associated with the flu. The effectiveness of the flu vaccine is intrinsically linked to the accuracy of scientific predictions regarding the dominant circulating strains each year, a complex endeavor in viral evolution.
However, a compelling and evolving narrative is emerging around the "indirect benefits" of these vaccines. These are the positive health outcomes that extend beyond the prevention of the specific disease against which a vaccine was designed. As Dr. William Schaffner, an infectious disease specialist at Vanderbilt University Medical Center, explains, research in this area has "accumulated and accelerated in the last 10 years," revealing a broader protective scope for immunizations.
Some of these indirect effects have been observed for decades, while others are supported by more recent studies, with their full implications still under investigation. The RSV vaccine, for instance, only became widely available in 2023, making its long-term indirect benefits a subject of ongoing research. Nevertheless, the findings thus far are described as "very consistent" by Dr. Stefania Maggi, a geriatrician and senior researcher at the National Research Council Neuroscience Institute in Padua, Italy.
Dr. Maggi, lead author of a comprehensive meta-analysis published in the journal Age and Ageing, found a notable reduction in dementia risk following vaccination against various diseases. This research suggests that "vaccines are key tools for promoting healthy aging and preventing physical and cognitive decline" by triggering these beneficial "chain reactions."
Despite this growing evidence, a significant portion of older adults remain unvaccinated. This is particularly concerning given that their immune systems naturally weaken with age, and the prevalence of chronic health conditions further elevates their susceptibility to infectious diseases. Data from the Centers for Disease Control and Prevention (CDC) in mid-December indicated that approximately 37% of older adults had not yet received their annual flu shot. Only 42% had ever been vaccinated against RSV, and less than a third had received the most recent COVID-19 vaccine. Vaccination rates for pneumococcal disease also remain suboptimal, with an analysis in the American Journal of Preventive Medicine estimating that only 12% of individuals aged 67-74 and just 8% of those over 75 had received the recommended pneumococcal vaccine since the updated recommendations in 2022.
The most robust evidence for indirect benefits, spanning 25 years, points to a significant reduction in cardiovascular risk following influenza vaccination. Healthy older adults who receive the flu vaccine exhibit a substantially lower risk of hospitalization for heart failure, as well as for pneumonia and other respiratory infections. Furthermore, flu vaccination has been consistently associated with a reduced risk of heart attack and stroke. It is important to note that many of these foundational studies were conducted before the availability of the more potent influenza vaccines currently recommended for older adults, suggesting that the protective benefits may be even greater with contemporary vaccines.
The question naturally arises: could vaccines against other respiratory illnesses, such as RSV, offer similar cardiovascular benefits? A large-scale study in Denmark involving older adults found a nearly 10% reduction in cardiorespiratory hospitalizations (those involving both the heart and lungs) among vaccinated individuals compared to a control group. While this reduction was significant, the decrease in hospitalizations specifically for cardiovascular diseases and strokes did not reach statistical significance. 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 could be due to a short follow-up period or limitations in diagnostic testing. However, she expresses optimism, stating, "I don’t think RSV will behave very differently from the flu. It’s still too early to have all the data on RSV, but I think it’s going to show the same effect, maybe even greater."
Vaccination against COVID-19, another dangerous respiratory illness, has also been linked to 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, researchers reported an association between this vaccine and lower rates of dementia, even with an earlier, less effective version of the vaccine that has since been superseded by Shingrix, approved in 2017. The majority of studies exploring indirect benefits are observational, as ethical considerations prevent researchers from withholding a safe and effective vaccine from a control group that could potentially contract the disease.
This observational nature means results could be influenced by "healthy volunteer bias," where vaccinated individuals may also engage in other healthy behaviors that differentiate them from their unvaccinated counterparts. While researchers strive to adjust for factors like age, sex, health status, and education level, Dr. Maggi cautions, "We can only say there is a strong association between the vaccine and lower dementia rates, but not a causal relationship."
To address this, researchers at Stanford leveraged a "natural experiment" in Wales that occurred in 2013. At that time, the first shingles vaccine, Zostavax, was offered to individuals under 80 years old, with those aged 80 and above being ineligible. Over a seven-year period, dementia rates among those eligible for the vaccine decreased by 20% – despite only half of them actually receiving it – when compared to those who missed eligibility by mere days. As Maggi points out, "There’s no reason to think that people born a week earlier were different from those born a few days later." This study provides stronger evidence for a potential causal link.
Further research from Australia and the United States has also identified a correlation between shingles vaccination and a reduced likelihood of developing dementia. In the meta-analysis conducted by Maggi’s team, several childhood and adult vaccines demonstrated similar indirect effects. "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 encompassing over 104 million participants in Europe, Asia, and North America, shingles vaccination was associated with a 24% reduction in dementia risk. The influenza vaccine showed a 13% reduction, and the pneumococcal vaccine was linked to a 36% lower risk of Alzheimer’s disease. The Tdap vaccine (tetanus, diphtheria, and pertussis) was associated with a one-third reduction in dementia risk, and it is recommended for adults every 10 years, often administered when grandchildren are born, as newborns are not fully protected in their early months.
Other researchers are actively investigating whether the shingles vaccine might also reduce the risk of heart attacks and strokes, and whether COVID-19 vaccination could improve survival rates for cancer patients.
The underlying mechanisms driving these additional vaccine benefits are primarily hypothesized to revolve around inflammation. When the immune system mounts a response to an infection, it triggers an inflammatory process. "Damage is generated in the environment surrounding the body’s cells, and it takes time to return to normal," Dr. Chu explains. The effects of inflammation can persist long after the initial infection, potentially creating conditions conducive to other infections or contributing to heart attacks and strokes through blood clot formation in narrowed blood vessels. "If you prevent the infection, you also prevent that downstream damage," Chu added.
Hospitalization itself can be a significant risk factor for cognitive decline and other health issues in older adults, leading to loss of strength, mobility, and the potential for delirium. Therefore, vaccines that help avert hospitalization could play a role in delaying or even preventing cognitive deterioration.
Concerns have been raised that a shifting national policy landscape, with some officials questioning the necessity of certain childhood vaccines, could inadvertently contribute to lower vaccination rates among older adults. This trend is worrying, as it not only means missing out on the increasingly recognized indirect benefits of vaccination but also leaves individuals vulnerable to preventable and treatable diseases. Dr. Schaffner, a former member of the CDC’s Advisory Committee on Immunization Practices, expressed concern, stating, "The current national policy on vaccination is, at best, ambiguous, and in some aspects appears anti-vaccine. All of us working in public health are extremely concerned."