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Researchers who tracked cases of dementia in Welsh adults have uncovered the strongest evidence yet that the shingles vaccination reduces the risk of developing the devastating brain disease.
Health records of more than 280,000 older adults revealed that those who received a largely discontinued shingles vaccine called Zostavax were 20% less likely to be diagnosed with dementia over the next seven years than those who went without.
Pascal Geldsetzer, at Stanford University, said: “For the first time we are able to say much more confidently that the shingles vaccine causes a reduction in dementia risk. If this truly is a causal effect, we have a finding that’s of tremendous importance.”
The researchers took advantage of a vaccination rollout that took place in Wales more than a decade ago. Public health policy dictated that from 1 September 2013, people born on or after 2 September 1933 became eligible for the Zostavax shot, while those who were older missed out.
The policy created a natural experiment where the older population was sharply divided into two groups depending on their access to the vaccine. This allowed the researchers to compare dementia rates in older people born weeks apart but on either side of the vaccine eligibility divide.
After accounting for the fact that not all those eligible for the vaccine received it, the researchers found vaccination led to a 20% reduction in dementia risk, with the strongest effect in women. Anupam Jena, a professor of healthcare policy at Harvard Medical School, said the implications were profound.
Dementia affects more than 55 million people globally and is the leading cause of death in the UK. One in three will develop the condition in their lifetime, and while drugs that slow the disease have recently been approved, there is no cure.
When people contract chickenpox the virus remains dormant in their nerve cells for life. But the virus can reactivate and cause shingles in older people whose immune systems are waning, or in individuals with weakened immunity.
The latest work, published in Nature, is not the first hint that shingles vaccines might shield against dementia. When Zostavax was rolled out in the US in 2006, several studies found lower rates of dementia in people who received the shots. Last year, Oxford researchers reported an even stronger protective effect in people who received Shingrix, a newer vaccine. Geldsetzer is now looking for philanthropic and private foundations to fund a randomised clinical trial to confirm any benefits.
It is unclear how shingles vaccines might protect against dementia, but one theory is that they reduce inflammation in the nervous system by preventing reactivation of the virus. Another theory is that the vaccines induce broader changes in the immune system that are protective. These wider effects are seen more often in women, potentially explaining the sex differences in the study.
In an accompanying article, Jena wrote: “Although it is still unclear precisely how herpes zoster vaccination lowers the risk of dementia, the implications of the study are profound. The vaccine could represent a cost-effective intervention that has public-health benefits strongly exceeding its intended purpose.”
Julia Dudley, the head of research at Alzheimer’s Research UK, said the study strengthened the emerging link between shingles vaccination and reduced dementia risk. “While previous studies suggested an association, this research offers stronger evidence of a direct link, with greater benefit observed in women.
“It’s unclear exactly how the shingles vaccine might influence dementia risk. It may reduce inflammation, support the immune system in ways that protect the brain or involve other mechanisms. It’s important to note that this study looked at the Zostavax vaccine rather than Shingrix, which is now more commonly used.
“Understanding this link better, including the reason for any differences between men and women, could open new avenues for dementia prevention and treatment,” she said.
Maxime Taquet, whose Oxford study found a reduced dementia risk after Shingrix vaccination, said adjuvants in that vaccine, which make the immune response more potent, may play a role. Both studies “provide strong support for the hypothesis that shingles vaccination reduces dementia risk, with the newer recombinant vaccine offering superior protection,” he said. “A key question is whether this enhanced protection is due to improved shingles prevention or the adjuvant’s immunological effects.”
