Previously, I wrote about a study that showed that the shingles vaccine decreased the risk of cognitive decline like dementia and Alzheimer’s disease. However, that study only showed that the vaccine reduced the risk, but we didn’t know if it directly decreased the risk of cognitive decline or if shingles increased the risk.

A new study published in a leading Alzheimer’s disease journal shows that shingles increases the risk of cognitive decline which fits well with the previous study that showed that the vaccine reduced the risk. This provides more evidence that the shingles vaccine has benefits beyond just preventing shingles.

This post will examine the new research and list the key findings.

What is shingles?

One of the consequences of contracting chickenpox, caused by the Varicella zoster virus (VZV), is that the body’s immune system does not destroy the virus. 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 hangs out there, 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 later 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 name based on biological binomial nomenclature. We now know that the virus Varicella zoster causes both chickenpox and shingles.

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 causes. Once shingles appear, it can be painful, depending on the location of the outbreak. It can cause blindness, disfigurement of the infected area, 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 appear like acne or other skin conditions, 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.

Almost all individuals in the US aged 50 years and older have been infected with VZV and are therefore at risk for shingles. There’s a growing body of evidence that herpes viruses, including VZV, can influence cognitive decline.

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 another way to prevent 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 contract chickenpox. Second, children who have received the chickenpox vaccine should never contract shingles.

New shingles and cognitive decline paper

In a paper published on 14 August 2024 in Alzheimer’s Research and Therapy, Sharon Curhan, MD, Channing Division for Network Medicine, Brigham and Women’s Hospital, Boston, MA, and colleagues studied149,327 participants from three large cohorts — the Nurses’ Health Study, Nurses’ Health Study II, and Health Professionals Follow-Up Study — who completed health status surveys every two years, including questions about shingles episodes and cognitive decline. They compared those who had shingles with those who didn’t.

Here is the key result — an episode of shingles is associated with approximately 20% higher long-term risk of subjective cognitive decline. The researchers also found that the risk was higher among men who were carriers of the gene APOE ε4, which is linked to cognitive impairment and dementia. That same association wasn’t present in women.

The authors concluded:

Data from three large independent cohorts of women and men showed that HZ was associated with higher long-term risk of SCD, and the risk may differ by APOE ε4-carrier status.

Summary

This new study fortifies the study that showed that individuals who had received the shingles vaccine had a lower risk of cognitive decline, such as dementia and Alzheimer’s disease. Now we know that not only does the shingles vaccine reduce the risk but getting shingles increases the risk.

There is growing evidence linking VZV to vascular disease, called VZV vasculopathy, in which the virus causes damage to blood vessels in the brain or body. Curhan and other researchers at Brigham and Women’s have also found that shingles is linked to a higher long-term risk of stroke and heart disease.

The shingles vaccine should be a priority for all individuals because it prevents shingles itself. But if it also reduces the risk of cognitive decline that’s almost as important.

Citations

• Curhan SG, Kawai K, Yawn B, Rexrode KM, Rimm EB, Curhan GC. Herpes Zoster and Long-Term Risk of Cardiovascular Disease. J Am Heart Assoc. 2022 Dec 6;11(23):e027451. doi: 10.1161/JAHA.122.027451. Epub 2022 Nov 16. PMID: 36382961; PMCID: PMC9851464.
• Oriá RB, Smith CJ, Ashford JW, Vitek MP, Guerrant RL. Pros and Cons of APOE4 Homozygosity and Effects on Neuroplasticity, Malnutrition, and Infections in Early Life Adversity, Alzheimer’s Disease, and Alzheimer’s Prevention. J Alzheimers Dis. 2024 Aug 1. doi: 10.3233/JAD-240888. Epub ahead of print. PMID: 39093076.
• Yeh TS, Curhan GC, Yawn BP, Willett WC, Curhan SG. Herpes zoster and long-term risk of subjective cognitive decline. Alzheimers Res Ther. 2024 Aug 14;16(1):180. doi: 10.1186/s13195-024-01511-x. PMID: 39138535; PMCID: PMC11323373.