A unique Welsh health policy provided a rare opportunity for researchers.
The study, led by researchers at Stanford Medicine and recently published in the journal Nature, strengthened evidence that shingles vaccination may lower dementia risk.
In 2013, Wales began a shingles vaccination program that made individuals eligible for the shingles vaccine when they reached age 79. Those who were 80 or older when the program started were ineligible, though.
The Stanford-led study found that Welsh people who received the shingles vaccine were 20% less likely to develop dementia over a seven-year period compared with the Welsh people who were ineligible for the vaccine.
Shingles is an infection involving a painful rash that is caused by the same virus as chicken pox. After someone has chicken pox, the virus enters their body through the nervous system and remains dormant for years.
The senior author of the recent study, Dr. Pascal Geldsetzer of Stanford, took note of Wales’ program and realized it provided an opportunity for a “natural experiment.” The program is as close to a randomized controlled clinical trial (which is considered the gold standard for scientific studies) as you could get without conducting one, Geldsetzer says.
Geldsetzer and his fellow researchers analyzed the medical records of adults who were dementia-free at the start of the Welsh vaccination program.
They focused on those who turned 80 just before the program started (and thus would’ve been ineligible for the shingles vaccine) and those who turned 80 just after the program started (and thus were eligible for the vaccine). That allowed the researchers to compare two groups of people who were similar aside from the fact that one group could not receive the vaccine.
Previous studies had a major bias: They relied on participants who were already vaccinated and therefore, researchers say, already more health-conscious. Generally speaking, this makes them more likely to have a better diet and exercise routine, which also influence dementia risk.
The Stanford-led study eliminated this bias.
The study also supports an emerging theory that viruses affecting the nervous system can increase the risk of dementia, not just the virus that causes shingles.
The Stanford-led study only reviewed the effects of the older shingles vaccine, Zostavax. The newer shingles vaccine, Shingrix, was not yet available when Wales’ shingles vaccination program started.
A 2024 study, however, analyzed the effects of Shingrix and found it is associated with a 17% lower risk of dementia when compared with Zostavax.
In the United States, Zostavax is no longer available, and the Centers for Disease Control and Prevention recommends Shingrix to adults 50 and older.
Still, the Stanford-led study provides further support for the association between shingles vaccination in general and lower dementia risk.
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