HIQA review finds studies suggesting a link between the two conditions, but no randomised clinical trials proving causation
Current evidence is not yet strong enough to show that a shingles vaccine reduces the risk of dementia, a new Irish report has found.
While the review of international research by the Health Information and Quality Authority (HIQA) noted that some studies suggested that contracting the herpes zoster virus – commonly known as shingles – could increase the risk of getting dementia, others found no clear link between the two conditions.
There has been no randomised controlled trial to determine a causation between shingles vaccination and the prevention of dementia. However, HIQA found ten non-controlled studies which all reported a protective association, with the authors concluding that the vaccine reduced the risk of dementia.
However, the health watchdog noted: “It is unclear if any reduced risk of dementia reflects prevention or delay in onset, and the extent to which such protection wanes over time. This would be an important factor in estimating the optimal age for vaccination.”
The review follows a 2024 health technology assessment of the Herpes Zoster vaccine, which found that adding the inoculation to the national immunisation programme for adults would be ‘not cost effective’ at that year’s market prices.
This new scoping review was conducted in response to emerging evidence reporting a link between shingles vaccination and lower dementia risk.
“Dementia is a major public health challenge, and even modest reductions in risk could have meaningful benefits for individuals, families, and society,” said HIQA’s chief scientist Dr Conor Teljeur.
“Recent studies report a protective association between vaccination and dementia. We need to understand the magnitude of any benefit of the shingles vaccine and the extent to which it applies independent of other vaccinations, such as for flu.”
HIQA advised that the findings of it scoping exercise should be considered in the planned review of any new evidence of the clinical effectiveness and safety of shingles vaccination since the publication of its 2024 HTA.
“While the current evidence base lacks robustness and causal certainty, the broadly consistent direction of association suggests that shingles vaccination as well as other routine adult vaccinations may offer some benefit against dementia,” the report concluded.
“This evidence should be considered alongside an updated review of the clinical effectiveness of shingles vaccination, informing whether the impact on healthcare resources needs to be re-assessed.”