Can The Shingles Vaccine Delay Dementia? Key Takeaways

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It’s not just about shingles anymore—this vaccine could have brain benefits.

A news article summarizing a scientific publication earlier this year (April 2025) in the Journal of American Medical Association caught my attention – and maybe yours too – with  the headline: "Shingles vaccine may directly guard against dementia, study hints". It certainly created a stir in the medical community. 

So I thought I'd summarize some previous studies to give you the big picture.  

What made scientists dig deeper into this brain health topic? 

Medical researchers in China had noticed a slight trend in increased risk of dementia in people who had previously contracted certain viral infections, such as shingles.  

This strongly suggested that these infections were the cause of (or contributors to) dementia, possibly by way of neuro-inflammation and/or diseased blood vessels in the brain.  

In fact, other similar studies led to the 'viral infection' hypothesis of the cause of Alzheimer's disease.  This hypothesis supposes that viral infections (specifically the herpes viruses - a family of viruses that includes varicella-zoster virus – the germ behind chickenpox and shingles) contribute to the development of the Alzheimer's, which is the most common form of dementia. So researchers obviously wanted to know if being vaccinated against these viruses would reduce that risk. 

In 2022 a team of Chinese researchers analyzed the results of 17 studies including over 1.8 million people (conducted by researchers around the world) that compared the risk of dementia in vaccinated versus unvaccinated populations.

What did they find? 

📊 Some common vaccinations were associated with a subsequent 35% overall decrease in the risk of dementia. (Influenza, herpes zoster [shingles], Tdap, hepatitis A, hepatitis B, typhoid, and rabies)   

📊 The more vaccinations a person received, the lower their risk of dementia, including Alzheimer's.  

The problem with this analysis however, was that all study subjects had chosen to be vaccinated and were therefore biased towards a more healthy lifestyle in general than those who chose to remain unvaccinated. In other words, people who were not vaccinated may been impoverished, may not have been aware of any benefits of vaccinations, may have been in poor health, or may have a more sedentary lifestyle etc. 

Scientists had to find a better way to look at this data. 

So in 2023, another team of researchers decided to try to refine this type of analysis to control for the bias towards the type of people choosing to be vaccinated. Unfortunately, it's really hard to design a study where you recruit a bunch of people and tell them that half of them will be vaccinated and the other half will get saline only – it's a bit unethical – so they did the next best thing. This team focused on a population of people who had been vaccinated against the herpes zoster (shingles) virus. For the science geeks: the varicella zoster virus  – the one that initially causes chickenpox – is contracted at a young age but resurfaces later in life as the herpes zoster virus to cause shingles (two completely different diseases but the same family of virus).  

How was this deep dive different?  

They analyzed health records of a population of older people in Wales who did or did not receive the herpes zoster vaccine (Zostavax) for shingles prevention. Their eligibility for getting the jab was based on an individual’s exact date of birth. People who were born before Sept.2 1933 were not eligible because of their advanced age. The ineligible people may have wanted to get the vaccine, but weren't allowed, and thus, the two populations of people were very similar in lifestyle and health status, etc. The researchers then analyzed health records (which included a cognitive assessment) of people born within a week on either side of the cutoff date, (so they were also essentially the same age) and analyzed both vaccinated and unvaccinated groups. 

What did they find? 

📊 After following these two populations for 7 years, the people who received the herpes zoster vaccine were 20% less likely to develop a dementia diagnosis.  

📊 The protective effects from the vaccine for dementia were far stronger among women than men. (It should be noted here that both shingles and Alzheimer's Disease occur more commonly in women compared to men, but the authors didn't expand on the possible reason for the enhanced protection for women).  

📊 Their analyses agreed with the 2022 study and strongly suggested that vaccinating against this virus could potentially prevent new onset of dementia. 

This was a unique natural randomization but the authors recognized that more accurate diagnoses of dementia were needed, and a longer follow up time was necessary to capture the participants who may have developed dementia later. Additionally, socio-economic and behaviour biases were still a problem.  So they kept refining their methods of data collection. 

One Step Closer 

In 2024, the same group published their findings from a detailed analysis of health records from an Australian population of older adults (aged 70-79) who were eligible for a FREE vaccine (which eliminated some of the socio-economic and lifestyle bias), compared to the 'control group' of older adults that were not eligible (younger than 70 and older than 79) for the free vaccine. This created two groups: individuals born just before vs just after the date-of-birth eligibility threshold, such that participants in both groups were essentially the same age.  Both groups were followed for 7.5 years (the same amount of time, not longer, as the previous study). The authors noted: "The key strength of this quasi-experiment is that one would not expect that these comparison groups who differ in age only minutely would, on average, differ in any health characteristics and behaviours."  

What did they find? 

📊 After eliminating as many biases as they could, their refined study showed that having the vaccination decreased the probability of a new dementia diagnosis by only 1.8%, compared to 20% and 35% in the previous studies. (In other words, they crunched their numbers with a bigger hammer to get better statistical analyses – which likely contributed to the smaller effect.

📊 They also believed that they under-diagnosing the number of dementia cases, based on how the health care providers in Australia collected their cognitive health information. (Meaning that the effect could actually be much larger than 1.8%.) 

While the two most recent analyses were conducted on two different populations (Australia and Wales), which added to the strength to their results, they still recognized that proper randomized trials are needed to figure out which age population was the most appropriate to look at (they considered people in their 70s only) and the most beneficial time window for administration of the herpes zoster vaccine to prevent or delay dementia (should it be decades earlier?). 

Bottom Line  

The good news: three extremely large and well-thought out studies showed at least some reduction in risk of dementia from being vaccinated against shingles, which is compelling. If future clinical trials confirm the results, it could be a cost-effective way of reducing the risk of dementia. 

The bad news: the more controlled and refined the studies became, the smaller the reduction in risk of dementia, suggesting that there may be no benefit seen if/when the clinical trials are done with double-blinded, placebo-controlled methods. In fact, a 2022 smaller observational study of health records (similar to the ones above) on a Danish population found that there was 0% protective effect of the vaccine.  

My Final Thoughts 

I love that scientists are chasing down answers to really important questions like this; because even though there may ultimately be no reduction in the risk to the general population of developing dementia after being vaccinated, there is a reason for their observation of a protective effect. Whether it's that people with healthy lifestyles and higher socio-economic status tend to avoid dementia (no surprise there), or that the vaccine actually does in some way guard against the inflammatory and vascular origins of dementia, there is compelling rationale to continue to investigate this. Although none of the studies above were able to pinpoint a specific reason for the potential link between the shingles vaccine and a reduced risk of dementia, their overall observations provide some strong motivation to keep looking for links. 

Regardless, I'm a believer. I'm making the decision to do everything I can to avoid dementia, and that includes getting the jab (yep, I did it) with the primary intention of avoiding shingles and the possible benefit of remaining dementia-free.