A new study shows that there might be a lower risk of dementia for those who have received the shingles vaccine. Although preventing shingles itself is a huge benefit of the vaccine, preventing dementia could be a “bonus” side effect.

As I usually do, let’s take a look first at what is shingles and then the paper itself.

What are shingles?

One of the consequences of contracting chickenpox, caused by a virus called Varicella zoster, is that the virus is not destroyed by the body’s immune system. Once the symptoms of chickenpox disappear, the virus hides (it does not do this consciously, it’s a virus) in the dorsal root ganglion, a bundle of nerve fibers at the bottom of the spinal column. The virus just hangs out there, basically hidden from the body’s immune system.

We are not sure why it does this, but it may be an evolutionary adaptation to survive until a later point in time so that it can reproduce and reinfect the victim.

Even though the body generated an immune response to the original zoster virus infection, several years or decades after the initial infection, the adaptive immune response against the virus wanes or disappears. Due to other unknown factors, possibly stress or other infections like COVID-19, the Varicella zoster virus “moves” along the nerve bundles and begins a secondary infection with much more serious consequences to the individual.

This second infection is called herpes zoster, more commonly known as shingles. This infection usually happens when the patient is older than 50, although it can happen at any time, occasionally even in young adults. 

Despite both chickenpox and shingles being caused by the same virus, shingles were given a different name, herpes zoster, probably because it was originally thought to be caused by a similar, but unrelated virus. However, herpes zoster is not a formal biological binomial nomenclature, and we now know that both chickenpox and shingles are caused by the same virus, Varicella zoster.

What can be said about shingles is that it’s an entirely unpredictable disease. It appears at random points in time in response to unknown variables. Once shingles appear, it is incredibly painful, depending on the location of the outbreak. It can cause blindness, disfigurement of the area infected, permanent pain, and other conditions.

Shingles can be treated with antiviral drugs, but only if the infection is recognized and treated within 24-72 hours, a time frame that might not allow most individuals to get to their doctor. The initial symptoms may even appear like acne or some other skin condition, which many people might ignore. After 72 hours, the disease has to run its painful and dangerous course. The pain of shingles may last for weeks, months, or even years after the blisters have healed – this is not a trivial disease.

The only way to prevent a shingles infection is to boost the immune system with a new vaccine against the zoster virus. Shingrix (a shingles vaccine, sometimes called the zoster vaccine, available in the USA) is a relatively new, safe, and effective vaccine.

There is one other way to not get shingles — never get chickenpox in the first place. And we have a vaccine for that, the chickenpox (or varicella) vaccine.

So let’s be clear about a couple of things. First, you are only at risk for shingles if you contracted chickenpox. Second, children who have been vaccinated against chickenpox probably will never contract shingles.

Shingles vaccine and dementia paper

In a preprint published in the preprint server medRxiv, Pascal Geldsetzer, MD, MPH, Ph.D., of Stanford University in California, and co-authors, analyzed 282,541 adults born from 1 September 1925 to 31 August 1942 who were registered with a primary care provider when the shingles vaccine program in Wales started on Sept. 1, 2013. In Wales, if you were born before 2 September 1933, you could not get the shingles vaccine and would remain ineligible for the vaccine for life. If you were born on or after that date, you could get the zoster vaccine.

Because of this cutoff date, the effects of the zoster vaccine, beyond preventing shingles, constituted a “natural” experiment. It was a form of a randomized clinical trial with a control group who did not receive the vaccine and another group who did.

Here is the key result — individuals who received the herpes zoster vaccine (Zostavax, which is no longer available in the USA) reduced the probability of a new dementia diagnosis over 7 years by 3.5 percentage points. That is a statistically significant reduction in dementia diagnosis.

This type of result with shingles is not surprising. One study has shown that 45 viral exposures are linked to an increased risk of dementia. Another study has shown that herpesvirus 6A and 7 have been found in postmortem tissue samples of people with Alzheimer’s disease at levels up to twice as high as non-Alzheimer’s samples.

In other words, there is a growing body of evidence that viral infections increase the risk of dementia and Alzheimer’s disease. Even the flu has been shown to be linked to a higher risk of dementia, and the flu vaccine may reduce the risk of Alzheimer’s disease by over 40%.

Summary of shingles vaccine and dementia

Because this study is a preprint and has not been properly peer-reviewed, I am going to be tentative in my evaluation of the article. But the fact that many other studies have provided a growing body of evidence that various viral infections increase one’s risk of dementia and Alzheimer’s disease, I think preventing those diseases has a long-term benefit that we are just beginning to understand.

Will the shingles vaccine prevent dementia in all cases? No, but it reduces the risk of dementia. And eventually, we will compare groups of individuals who received all of their vaccines to unvaccinated individuals, and we probably are going to see a significant reduction in the risk of dementia in the vaccinated group.

Again, preventing dementia is just a bonus. Shingles is an extremely painful and disfiguring disease, and getting the vaccine to prevent that disease is extremely important, especially for those who are 50 years old and above.

Get the vaccine, it could save your life and your brain.

Citations

• Levine KS, Leonard HL, Blauwendraat C, Iwaki H, Johnson N, Bandres-Ciga S, Ferrucci L, Faghri F, Singleton AB, Nalls MA. Virus exposure and neurodegenerative disease risk across national biobanks. Neuron. 2023 Apr 5;111(7):1086-1093.e2. doi: 10.1016/j.neuron.2022.12.029. Epub 2023 Jan 19. PMID: 36669485; PMCID: PMC10079561.
• Readhead B, Haure-Mirande JV, Funk CC, Richards MA, Shannon P, Haroutunian V, Sano M, Liang WS, Beckmann ND, Price ND, Reiman EM, Schadt EE, Ehrlich ME, Gandy S, Dudley JT. Multiscale Analysis of Independent Alzheimer’s Cohorts Finds Disruption of Molecular, Genetic, and Clinical Networks by Human Herpesvirus. Neuron. 2018 Jul 11;99(1):64-82.e7. doi: 10.1016/j.neuron.2018.05.023. Epub 2018 Jun 21. PMID: 29937276; PMCID: PMC6551233.