I generally wouldn’t write about herpes zoster and dementia, which recently appeared in a peer-reviewed article. Such a topic is mostly outside of my interest area. Then a thought hit my reptilian brain — anti-vaxxers might use this information to claim that the shingles vaccine, which prevents herpes zoster (the more formal name for shingles), might increase the risk of dementia.
So, this article is here just in case you run into that pathetic argument. In no way would I advocate not getting the shingles vaccine because of its supposed relationship with dementia.
Let’s take a look at this new article and how we should look at whether the herpes zoster vaccine and dementia might be related.
What are shingles?
One of the consequences of contracting chickenpox, 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. Of course, viruses are very simple organisms (and some biologists will debate that it’s not a living organism), so complex behavior may be pushing our understanding of a virus.
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 wanes, weakens, or disappears. Due to other unknown factors, possibly stress or other infections, the zoster virus “moves” along the nerve bundles, then causes the second infection with much more serious consequences to the patient.
This second infection is called herpes zoster (see Note 1) and is 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.
What can be said about shingles is that it’s an entirely unpredictable disease. It really appears at random points in time in response to unknown causes. 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 is the currently recommended shingles vaccine available in the USA and many other countries. According to the CDC:
CDC recommends that adults 50 years and older get two doses of the shingles vaccine called Shingrix (recombinant zoster vaccine) to prevent shingles and the complications from the disease. Adults 19 years and older who have weakened immune systems because of disease or therapy should also get two doses of Shingrix, as they have a higher risk of getting shingles and related complications.
If I had contracted chickenpox, I’d ask for the vaccine even in my 40s, just to prevent the more severe shingles attack. But that’s not medical advice.
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, ever contract shingles. Is this clear? The chickenpox vaccine prevents chickenpox AND shingles.
The herpes zoster and dementia article
In a paper published on 8 June 2022 in Neurology, Sigrun Alba Johannesdottir Schmidt, MD, PhD of Aarhus University Hospital in Denmark, and colleagues used Danish medical registries to identify 247,305 people who had visited a hospital for herpes zoster or were prescribed antiviral medication for herpes zoster over a 20-year period of time. The researchers then matched them to 1,235,890 people who did not have herpes zoster. For both cohorts, the median age was 64 years and 61% were women.
Here are their surprising results:
- Dementia had been diagnosed in 9.7% of herpes zoster patients and 10.3% of matched control persons (those without diagnosed herpes zoster) during up to 21 years of follow-up.
- Herpes zoster diagnosis was associated with a 7% decreased relative risk of all-cause dementia (HR=0.93).
- There was no statistically significant increase in long-term risk of dementia in any subgroup analysis except for one — there was a possible increase in the risk of dementia with herpes zoster that involved the central nervous system (HR=1.94). However, the population attributable fraction of dementia due to this rare complication is low (<1%), suggesting that universal vaccination against the varicella-zoster virus in the elderly has limited potential to reduce dementia risk, the investigators note.
Let’s be clear about these results — it’s a tiny decrease in dementia risk of contracting shingles, And it appears that there is a large increase in the risk of dementia with more severe cases of herpes zoster that attack the central nervous system.
Furthermore, the authors of the paper said that the slight decrease in the risk of dementia may be attributed to missed diagnoses of shingles in people with undiagnosed dementia. And the authors of the article were clear — they strongly encouraged older people to get the vaccine.
If someone is going to argue that the shingles vaccines, by preventing herpes zoster, increase the risk of dementia, there are several arguments against that:
- Shingles have a long list of complications that range from mild to severe and permanent. For anyone who has had shingles, it is not a trivial disease that can be ignored.
- The risk of dementia appears to be extremely low, and it is so small it could be explained by individuals who actually might have had herpes zoster but it was undiagnosed.
- Even if herpes zoster is linked to a lower risk of dementia, the risk is so small as it could be considered clinically insignificant.
I just know some anti-vaxxer who has not read this article in full will immediately proclaim that the shingles vaccine causes dementia. Sorry, but not even close. Since I’m going to get my Shingrix booster in a few weeks, my mind was not changed by this article even slightly. The risk of dementia is way too low (and can be explained by a lot of things unrelated to herpes zoster), and my fear of the complications of shingles is way too high.
- Despite both chickenpox and shingles being caused by the same exact virus, herpes zoster was given a different name probably because it was originally thought to be two different viruses. However, in this case, herpes zoster is not a formal biological binomial nomenclature.
- Johannesdottir Schmidt SA, Veres K, Sørensen HT, Obel N, Henderson VW. Incident Herpes Zoster and Risk of Dementia: A Population-Based Danish Cohort Study. Neurology. 2022 Jun 8:10.1212/WNL.0000000000200709. doi: 10.1212/WNL.0000000000200709. Epub ahead of print. PMID: 35676090.