(1) Dementia Risk Reduction 20% or More: Get your shingles shots if you are 50 or over (or 19 or over with immune deficiency)
A paper published in Nature on April 22, 2025 clearly showed that getting the old shingles shot (Zostavax) caused a 20% decrease in dementia (mostly Alzheimer's) in older people, during the next 7 years (at which time the study ended). Women benefited especially. And another study comparing the old and the new shingles vaccines found that the new one (Shingrix) was better not only for preventing shingles, but also for preventing dementia. Due to a "natural experiment," these findings show causality, not just correlation or association. In the U.S. at least, Shingrix is easy to get for people over 50 (no doctor's appointment needed, almost all insurance covers it, and these shots are good for life, they don't need to be repeated). About 30% of eligible adults have received shingles immunization already. People need to know that shingles shots reduce the risk of dementia as well as shingles - and there seem to be other important health benefits as well.
How Do We Know That the Shingles Shot Caused Less Dementia?
A study in Wales, in the UK, analyzed a natural experiment that proved a causal relationship. This study analyzed 7 years of patient data. What is a natural experiment, and why is it important?
Just observing that people getting the shingles shots developed less dementia would not prove that the shots caused the benefit. There might have been other causes. For example, perhaps the people who got their shots were more conscientious about their health and chose other healthy behaviors as well - and those, not the shots, caused less dementia. In that case, there would be no causality, which is important since then, getting more people to take the shots would not help them avoid dementia.
But the study in Wales had an arbitrary cut-off at age 80 (apparently to save money, and also due to the assumption that the shots were less effective after 80). Therefore, a large groups of people got the shots just before age 80, and another large group missed the shots because they were just above 80 (over 90,000 people were studied). So the groups could be compared, and there was no reason to expect any significant difference between them. Just to be sure, the researchers looked carefully, and could not find any difference. But there was a large discontinuity just at the cut-off, with those getting the shots having a 20% less risk of dementia developing during the 7 years of followup in this study.
This result was published in Nature, one of the most prestigious scientific journals in the world, on April 2, 2025. [However, the same result had also been published as a pre-print (before peer review), on May 25, 2023. Same overall result: 19.9% dementia reduction reported in the preprint, vs. 20.0% dementia reduction in the final publication almost two years later.]
What Is the Mechanism of Action?
No one knows for sure. But the most common cause of dementia is Alzheimer's. It is widely believed that Alzheimer's has multiple causes, one of which is chronic inflammation. And chronic inflammation can be caused by chronic infections - including by the herpes zoster virus, which causes chickenpox in children but then stays in the body for life.
This virus is controlled by the immune system until aging or another cause weakens immunity. Then it can become active again and cause shingles, which is more serious than chickenpox. In the U.S., more than 99% of the population had chickenpox as a child, so almost everyone has the shingles virus already.
How Do We Know That the New Shingles Shot Also Works to Prevent Dementia?
The study in Wales used the old shingles shot (Zostavax), which has been phased out and is no longer available in the U.S. because a better vaccine (Shingrix) has been developed. The new one was better for preventing shingles. But would it work against dementia as well?
The rapid transition from the old to the new vaccine in the U.S. created the opportunity for another natural experiment. This one showed that the new vaccine reduced dementia by 17% compared to the old vaccine; again, women benefited more than men. This study was published June 2024 in Nature Medicine. We can't just add 17% to 20% and estimate a 37% dementia reduction with the new (Shingrix) shot, because the two studies were different, including different measures of dementia. But it does seems reasonable to estimate that the series of two Shingrix shots reduces the risk of dementia by more than 20%, at least for the next 7 years of the study, and probably well after that.
The two Shingrix shots are usually given two to 6 months apart. In case you want to check in advance, the guidelines for who should or should not receive the shots are here.
Other Possible Benefits
The following are from observational studies, not controlled trials or natural experiments, so their conclusions are less definitive, but still worth noting.
A study has found that the (old) shingles vaccine helped prevent stroke also, published Feb. 2020.
And more recently, a large association study of 1.2 million Koreans found reduced Alzheimer's risk and reduced heart attack risk as well (published May 2025): "A large observational study published in the European Heart Journal in May 2025 found that people aged 50 and older who received the live zoster (shingles) vaccine had a 23% lower risk of cardiovascular events overall, including a 26% lower risk of major events like heart attack, stroke, or death from heart disease, and a 26% lower risk of heart failure. The protective effect was strongest in the first two to three years but lasted for up to eight years. These benefits were particularly noted among men, people under 60, and those with unhealthy lifestyle factors such as smoking, drinking, or inactivity. The study analyzed data from over 1.2 million Korean adults starting in 2012, making it one of the largest and most comprehensive to examine the link between shingles vaccination and heart outcomes."
This study also used the old shingles vaccine; it looked at results for up to 8 years, so the new (Shingrix) vaccine was not available when it started.
Risks of Shingles Shots
The main concern has been risk of GBS (Guillain-Barré syndrome). It is extremely rare; one estimate of the risk was three cases per million shingles vaccinations. Other studies of large datasets found too few cases to make any estimates, or no evidence for GBS at all. GBS can cause neuropathy and paralysis in some cases; most people fully recover, but that can take two or three years.