WASHINGTON—One of the largest studies ever conducted on the link between the varicella-zoster virus (VZV) vaccine and brain health reveals what it reveals. shingles -So-called “shingles”- Increased risk of dementia.
The study found that people who had multiple episodes of shingles had a higher risk of developing dementia in the years following their second outbreak than those who had only one episode.
The results of this study were recently published in a scientific journal natural medicine and provides additional evidence about the importance of getting vaccinated against VZV to protect the brain.
VZV is the causative virus. Chickenpox as a childthen remains latent in the nervous system. As we age, the virus reactivates, but “it’s usually defeated by the immune system,” said Pascal Geldsetzer, a professor at Stanford University School of Medicine and one of the study’s authors. However, in some cases, “the virus reactivates completely” and the typical symptoms of chickenpox, such as burning, itching, redness and painful blisters, develop, the researchers said.
The study found that two existing versions of the vaccine, with and without live virus, reduced the risk of disease recurrence and the development of dementia.
Researchers examined the electronic medical records of more than 100 million people in the United States from 2007 to 2023. After analyzing 400 different variables, including chronic conditions, demographic data, prescriptions, and doctor visits, researchers found that the risk of developing dementia was reduced by 27% to 33% in the three years following VZV vaccination.
The study also found that people who had multiple bouts of shingles had a 7% to 9% higher risk of developing dementia three to nine years after the second outbreak of the virus, compared to those who had only one.
The factors that influence dementia are multiple and complex, ranging from genetics to environment to viral infections. And although the number of people developing the disease is increasing, there are few effective treatments and no way to prevent it other than lifestyle changes.
Despite current promising research, the biological mechanisms explaining the effects of varicella-zoster virus on dementia remain unclear.
But there are some theories. One of these, the researchers say, is that despite not causing any visible symptoms, VZV “continuously” reactivates and directly affects parts of the brain associated with dementia.
Another theory involves the body’s natural immune response to infection, namely inflammation due to reactivation of the virus or its toxic effects. “This means that the virus itself is not directly attacking brain cells, but rather the problem stems from the brain’s inflammatory response to the presence of the virus,” said Anupam Jena, a physician at Massachusetts General Hospital.
Medications used to treat the painful symptoms of shingles may also be the cause. “I don’t know,” Jenna says.
However, the new study results show that people who receive two or more doses of the VZV vaccine are better protected against dementia, supporting previous research showing that receiving two doses of the Shingrix vaccine instead of one reduces reactivation of the varicella-zoster virus.
A deeper understanding of whether VZV contributes to neurodegeneration is an important step in finding better ways to treat dementia, said Patrick Schwab, lead author of the study and director of machine learning and artificial intelligence at biopharmaceutical company GSK, which makes one of the vaccines against the virus.
The study found that people who received two doses of Shingrix, a recent vaccine made by GSK that contains an inactivated portion of the virus, had an 18% lower risk of developing dementia in the five years after vaccination compared to those who received one dose of Zostavax, an older vaccine made using a live, attenuated shingles virus. (Zostavax withdrew from the North American market in 2020).
They also found that three years after vaccination, women over 50 who received Zostavax had a 35% lower risk of dementia. Similarly, women aged 80 to 89 who received two doses of Shingrix over the same time period had a 39% reduction in risk.
“The consistency of the results is quite remarkable,” says Schwab, who also heads GSK’s biomedical AI group. “And that’s ultimately what makes this research so interesting.”
A “complicating” aspect of the study, Schwab said, was that it could only measure cases of shingles that had been diagnosed and documented in medical records, meaning the study was “an indirect indicator of viral reactivation in general.”
The VZV vaccine is already one of the vaccines recommended for adults over 50 and people with weakened immune systems. Some doctors say the current evidence is already strong enough that they tell patients that preventing dementia is an added benefit and could be an additional reason to get vaccinated. Professor Jena said he recently spoke about the study to a group of medical residents who had never even heard of the link between shingles and dementia.
Jena reviewed a previous study co-authored by Gerdsetzer that followed more than 280,000 Welsh adults and found that those who received the VZV vaccine had a 20% lower risk of developing dementia over seven years.
The researchers note that the new study includes several elements that strengthen the certainty of its results and “provides very high-quality evidence.” For example, when researchers evaluated the effectiveness of both vaccines in preventing dementia, they found that the effects on the brain were not permanent and appeared to be related to a decline in the vaccines’ protection.
AM Barrett, professor and professor of neurology at the University of Massachusetts Medical School, says current tools to reduce dementia risk are limited and not very effective. Barrett, a neurologist and director of neurology services at the West Central Massachusetts Veterans Affairs Health System, worries that the issue will become politicized and influenced by growing distrust of medicine and growing hesitancy about vaccines.
“Unfortunately, people who are not personally affected by dementia may come to believe that this is an attempt to persuade people to take vaccines they don’t need,” Barrett says.
However, he added that VZV vaccination is inexpensive and widely available.
“We all hope to have five more years of playing with our grandchildren or five more years of driving,” Barrett said. “And those things are priceless.”
Written by Akira Johnson
(Translation: Jaime Arambide)
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