Shingles Vaccination Went With Fewer Dementia Diagnoses in Welsh Adults

CATEGORY: DISEASE PREVENTION

Could a vaccine against a rash change anyone’s odds of losing their memory? Shingles is that rash, painful and blistering, caused when the chickenpox virus wakes up after decades asleep in the nerves. Dementia is the slow loss of memory and thinking that eventually gets in the way of daily life. In Wales, older adults who received the shingles vaccine were about 20% less likely to be newly diagnosed with dementia over the following seven years.¹ The comparison group was otherwise similar adults who were never offered the shot. The measurement is the interesting part.

A Birthday in 1933 Decided Who Was Offered the Shot

Vaccine research keeps running into the same wall. People who choose to be vaccinated differ from people who do not, in health, in habits, in how easily they reach a clinic. Wales knocked that wall down by accident. When the country launched its shingles program in 2013, eligibility ran off a single date of birth. Anyone born on or after 2 September 1933 was offered the vaccine. Anyone born a day earlier was excluded for life.¹ Two people born a week apart on either side of that line are alike in age and background. One of them had access to the shot; the other never would. That is close to what a coin toss buys a randomized trial. Dementia diagnoses over the next seven years came from electronic health records in primary and secondary care, plus death certificates listing dementia as a cause.

Three or Four Fewer Cases per Hundred People

Being eligible for the vaccine and taking it went with a 3.5 percentage point drop in the chance of a new dementia diagnosis across those seven years, a 20% relative reduction.¹ Put a different way: for every 100 comparable older adults, roughly three to four fewer developed dementia. The association was distinctly stronger in women than in men, and the study could not say why. One detail matters for anyone reading the result today. This was Zostavax, the older live-attenuated version of the shingles vaccine, not the newer formulation many countries have since moved to.

Why a Sleeping Virus Might Reach the Brain

Several ideas are on the table and none of them is settled. The chickenpox virus, varicella-zoster by its proper name, never fully leaves the body. It hides in nerve cells and flares up as shingles when aging immune defenses drop their guard. Some researchers suspect that repeated reactivation, and the inflammation it stirs up in and around the brain, feeds the damage that shows up as dementia. Keeping the virus quiet might spare the brain some of that low-grade wear. A broader possibility is that the vaccine gives an aging immune system a general tune-up. None of this was tested here.

One Country, One Study, and the Same Trick Repeated in Australia

Because a birthday and not a personal decision set eligibility, this design gets nearer to cause and effect than the usual study that watches who happens to get vaccinated. It is still one study in one population. Dementia has many contributors, among them genetics, blood pressure and hearing loss, and no single shot stands between a person and all of them. The vaccine’s established job remains preventing shingles and its complications. The same birthdate trick was later run in Australia, where eligibility was linked to a 1.8 percentage point lower chance of a new dementia diagnosis over about seven years.² A 2025 review pooled 18 observational studies and roughly 9.4 million people. It found shingles vaccination associated with about 32% lower dementia risk, though the studies varied widely and cannot establish cause.³

Key Takeaways

• Eligibility for the shingles vaccine tracked with a 20% lower chance of a new dementia diagnosis over seven years, and the link was stronger in women.
• The birthdate cutoff makes this sturdier than an ordinary observational study. It is still one finding, and it is not proof that the vaccine prevents dementia.
• Preventing shingles is the vaccine’s confirmed benefit. Any effect on dementia risk remains promising and unconfirmed.

References

1. Eyting M, Xie M, Michalik F, et al. A natural experiment on the effect of herpes zoster vaccination on dementia. Nature. 2025;641(8062):438–446. link
2. Pomirchy M, Bommer C, Pradella F, et al. Herpes zoster vaccination and dementia occurrence. JAMA. 2025;333(23):2083–2092. link.
3. Marra F, Gomes K, Liu E, et al. Effects of herpes zoster infection, antivirals and vaccination on risk of developing dementia: a systematic review and meta-analysis. Human Vaccines & Immunotherapeutics. 2025;21(1):2546741. link.