A vaccine designed to prevent shingles may also be linked to a lower chance of dementia in older adults, according to a large U.S. study.
Researchers found that people who received Shingrix after entering a skilled nursing facility were less likely to be diagnosed with dementia over the next four years.
The study was led by Kaley Hayes, an assistant professor at Brown University’s School of Public Health, and was published in Annals of Internal Medicine. Researchers from Brown, the University of Delaware, the Providence Veterans Affairs Medical Center, and other institutions took part.
Shingles is a painful illness caused by the varicella-zoster virus. This is the same virus that causes chickenpox, and after the first infection it can remain hidden in the body for decades.
As people grow older, the immune system may become less able to keep the virus under control. The virus can then become active again and cause shingles, which often produces a painful rash and can sometimes lead to lasting nerve pain.
Shingrix is the newer shingles vaccine now widely used in the United States. It was introduced in 2017 and has replaced older shingles vaccines on the market.
Researchers have become interested in whether shingles vaccination may have benefits beyond preventing the infection itself. Several earlier studies involving older vaccines found that vaccinated people also appeared less likely to develop dementia.
The new study asked whether the same pattern could be seen with Shingrix. It also focused on older adults entering skilled nursing facilities, a group with a high risk of both shingles and cognitive decline.
The researchers examined Medicare information and electronic medical records from more than 5,500 facilities between 2017 and 2022. In total, they studied 509,926 people aged 66 or older who had not previously been diagnosed with dementia.
Only a small share of the participants received the vaccine after admission. Of the full group, 8,843 people received at least one dose of Shingrix, while the rest did not.
Four years later, dementia had been diagnosed in 18.8% of the vaccinated group. The rate was 24.6% among those who were not vaccinated.
After taking other factors into account, the researchers estimated that vaccination was associated with a 24% lower risk of dementia. Hayes said this difference could mean that roughly one in 17 dementia cases might potentially be avoided if the relationship is truly caused by the vaccine.
The team used a statistical method that attempts to copy some features of a randomized clinical trial. This approach can make comparisons between vaccinated and unvaccinated people more reliable when a real trial is not practical.
Still, this type of study has important limits. People who get vaccinated may differ from those who do not in ways that are difficult to measure, such as overall health, access to medical care, willingness to follow medical advice, or family support.
In this study, vaccinated adults were slightly younger and generally healthier. The researchers adjusted for these differences, but it is impossible to be certain that all important differences were removed.
This means the study cannot prove that Shingrix directly prevents dementia. It only shows that the two were linked in this large group of older adults.
Researchers are not yet sure why such a link might exist. Preventing shingles could reduce inflammation and stress on nerves, which might help protect brain function over time.
Vaccination could also affect the immune system in broader ways that are not yet fully understood. These ideas are possible explanations, but they remain theories and need more research.
The study is important because dementia affects millions of older adults and has major effects on independence, families, and health care systems. Even a modest reduction in risk could matter if it came from a vaccine that is already widely available for another reason.
However, the results should not be used to promise brain protection to patients. Shingrix is approved to prevent shingles, not dementia, and stronger evidence is needed before doctors can say it lowers dementia risk.
The researchers also reported funding from GlaxoSmithKline, the company that makes Shingrix. They said the company did not control the research methods, analysis, or publication decision, but readers should still consider this financial connection when reviewing the study.
Taken together, the findings are promising but not final. They strengthen the case for studying the connection between shingles vaccination and brain health, while also showing why carefully designed clinical research is still needed.
