Study says Shingles vaccine may have a role in preventing or limiting dementia

Getting vaccinated against shingles could protect you from getting dementia, or slow the progression of the disease, according to a new study.

New evidence from the US suggests that a shingles vaccine could reduce the risk of dementia by 20 per cent, or slow the progression of the disease, according to recent research from Stanford University. If these findings can be backed up in further research, the vaccine – which is readily available – could be used to help both prevent and treat dementia – a disease that is currently incurable and affects an estimate 57 million people globally.

The HSE report that approximately 64,000 people in Ireland have dementia, a number that is expected to more than double to over 150,000 by 2045. The prevalence is increasing due to the ageing population, while one-in-ten people diagnosed with dementia is under the age of 65.

In the latest research, researchers from Stanford University, the Heidelberg Institute of Global Health and Cardiff University examined electronic health records from the Secure Anonymised Information Linkage (SAIL) databank, finding that people who were eligible for the live shingles vaccine (Zostavax) were less likely to develop mild cognitive impairment, an early sign of dementia. Added to that, those who were already diagnosed with dementia were less likely to die from the disease.

The researchers used the UK National Health Service’s rollout of the shingles vaccination programme to design a natural experiment. The rollout made people eligible for the vaccine based on their date of birth and allowed researchers to compare two nearly identical groups – those born before and just after the eligibility cutoff.

The study, published in Cell, involved the analysis of health records from over 300,000 people in Wales between 2013 and 2022. Lead researcher Dr Haroon Ahmed, GP and Clinical Reader in Epidemiology at Cardiff University’s School of Medicine said that the results suggest that ‘shingles vaccine could potentially prevent early memory decline and slow disease progression.’ Because the vaccine is safe, affordable and already widely available, the findings could have major implications for public health. However, more research is needed to confirm the findings, both in terms of the potential protective effect against dementia, but also how and why it works.

This innovative study found that shingles vaccination both reduced new diagnoses of mild cognitive impairment, as well as reducing deaths due to dementia in those already living with the disease. The protective effect was stronger in women than men, a pattern previously noted in other studies of vaccine-related immune responses.

This study builds on previous studies by the same group of researchers that reported the ability of the shingles vaccine to prevent or delay dementia diagnoses.

A study published in Nature in 2024 linked a newer vaccine, Shingrix, with a protective effect against dementia. The risk of dementia after six years was 17 per cent lower in the group of adults over 65 that received Shingrix compared with the older vaccine, Zostavax, and was stronger for women (22 per cent ) than men (13 per cent). A randomised trial is being prepared to confirm these benefits.

Overall, those given Shingrix had a 23 per cent to 27 per cent lower risk of developing dementia than people who received other vaccines including flu, tetanus, diphtheria, or pertussis. While the mechanism of action is still not clear, possible mechanisms of action include that shingles vaccine prevents reactivation of dormant viruses such as varicella zoster and herpes simplex, which are thought to contribute to brain inflammation and the build-up of proteins in the brain linked to dementia. It is also possible that the vaccine provides a broader boost to the immune system, which counteracts the weakened immunity of older age.

In July 2024, the Health Information Quality Authority (HIQA) published a Health Technology Assessment (HTA) of shingles vaccination for adults. The HTA was undertaken at the request of the Department of Health following a recommendation from the National Immunisation Advisory Committee (NIAC). The HTA served to advise the Minister for Health on whether a shingles vaccination should be provided as part of the adult immunisation programme in Ireland.

HIQA’s Chief Scientist Dr Conor Teljeur said that the HTA, that included public consultation, considered aspects of shingles that included the burden of disease, patient aspects and social aspects.

“Our assessment concludes that the shingles vaccine is safe and effective, but that the benefit of the vaccine decreases over time. We found that, at the current vaccine price, adding shingles vaccination to the routine immunisation schedule for the general population aged 50 years and older would not be an efficient use of HSE resources.”

Feedback from public consultation highlighted the significant impact that shingles can have on individuals who experience longer-term complications. While shingles vaccines are available in Ireland – people must pay to be vaccinated. And it is not cheap. A two-dose course of Shingrix vaccine typically costs €480 – €490 (about €240 – €245 per dose).That includes the vaccine, consultation and administration.

The incidence and severity of shingles increases with age, with most cases occurring in people over the age of 50 years. People who are immuno-compromised are also at increased risk of shingles, and experiencing a severe disease course. HIQA assessed the impact of providing shingles vaccination for adults aged 50 years and older, and those aged 18 years and older who are at increased risk due to an immunocompromising condition or treatment.

Currently, this expensive vaccine is not available on the adult immunisation schedule. However, emerging evidence on the potential links between shingles vaccination and protection against dementia or slowed progression of disease, may cause this advice to change in the near future.

For now, what we can say is the health benefits of the shingles vaccines have the potential to go way beyond protecting us against shingles.

Author
Dr Catherine Conlon is a Senior Medical Officer in the Public Health Department, HSE, Cork.