CNN
—
Two new studies suggest that a vaccine to protect against a painful case of shingles might also benefit memory.
An estimated 98% of American adults have had chickenpox and are at risk of developing shingles; both are caused by the varicella-zoster virus, which belongs to the herpes family.
Herpes viruses are cunning and can hide quietly in the roots of nerves. They can reactivate during times of stress or illness, or any time a person’s immunity is weakened. This viral reactivation can cause shingles, a rash that opens in a line around the trunk or along the neck or face. The pain caused by shingles varies from person to person, but can range from tingling to burning, and can last for weeks.
A growing body of research suggests that some types of herpes viruses can also hide in the brain and become active again when the immune system lets its guard down. This could cause damage that can lead to dementia, the theory goes.
There is no cure for shingles, but antiviral medications can help treat it, and there are vaccines. In 2006, the first shingles vaccine was approved in the United States, Zostavax. In 2017, a more powerful vaccine, Shingrix, became available. The U.S. Centers for Disease Control and Prevention (CDC) has now released a report on the marketing of the shingles vaccine. recommends Shingrix over Zostavax for adults 50 years and older.
Zostavax contains a live but weakened form of the virus, but Shingrix contains only part of it: proteins found on its outer surface. Both vaccines work by teaching the body to recognize and fight the real virus when it starts causing problems.
In clinical trials, Shingrix was found to be 97% effective in preventing shingles, compared with 65% to 70% for Zostavax, depending on a person’s age. Shingrix also appears to offer longer protection, although this is still being studied.
The two new studies build on that history, examining the medical records of hundreds of thousands of people vaccinated with Shingrix and comparing how often they were diagnosed with dementia compared with people who received other types of vaccines.
It’s hard to eliminate all biases from observational studies like these, but the researchers tried to avoid one in particular: the healthy user effect. According to this effect, some people who are more likely to take care of their health are also more likely to engage in behaviors like going to the doctor regularly, exercising, and getting vaccinated. Similarly, unvaccinated people may be too frail or sick to be vaccinated, or may not have access to standard health care.
It is personal behavior or circumstances, more than any other specific factor, that determine an individual’s risk of contracting a number of diseases. If researchers try to compare vaccinated people with those who are not, they run the risk of comparing two fundamentally different groups of people and wrongly attributing any differences to vaccination alone.
The first study, published Thursday in the journal Nature Medicine, looked at dementia diagnoses in more than 100,000 people over the age of 65 who received the Zostavax vaccine and about 100,000 adults 65 and older who received the Shingrix vaccine.
One of the study’s authors, an immunologist, is a paid consultant for GlaxoSmithKline or GSK, the company that makes the Shingrix vaccine, but the researchers say the company played no role in their investigation.
“They actually didn’t even know we did it until the paper was accepted for publication because we wanted to do everything we could to avoid any potential conflict,” said study author Dr. Paul Harrison, a psychiatrist at the University of Oxford in the United Kingdom, speaking at a news briefing.
Researchers found that people who received Shingrix were 17% less likely to be diagnosed with dementia within six years of their injection than people who received the less effective Zostavax vaccine.
Vaccinated people didn’t completely avoid dementia, but it did appear to be associated with a delay in diagnosis. On average, the researchers found, that’s about 164 days without a diagnosis, or about five months longer, among people who eventually got it.
This type of study cannot prove that the vaccines were directly responsible for the differences between the groups. If further research proves that shingles vaccines do indeed protect memory and thinking, “at a public health level,” “This would not be a trivial discovery at all,” Harrison said.
Experts who were not involved in the study said it adds to a growing body of evidence suggesting that shingles vaccines may help protect the brain.
“There was already evidence that the older live vaccine was able to reduce the risk of Alzheimer’s disease,” Dr Andrew Doig, a biochemist at the University of Manchester, said in written comments.
It appears the new vaccine may be associated with an even greater reduction in risk, he said.
“This is a significant result, comparable in efficacy to recent antibody-based drugs against Alzheimer’s disease. “The disease,” Doig said.
The association was stronger in women who received Shingrix, although it is not clear why. Women had a 22% lower risk of developing dementia in the next six years compared with women who received Zostavax. Men had about a 13% lower risk.
The team then compared older adults vaccinated with Shingrix to those vaccinated against influenza and diphtheria, pertussis and tetanus. The risk of dementia in those vaccinated with Shingrix was 23% lower than in those vaccinated against influenza and 28% lower than in those vaccinated with the tDAP vaccine, supporting the idea that there is something unique about shingles vaccination that reduces the risk of dementia.
“It will be essential to study this apparent effect in more detail,” Dr Sheona Scales, director of research at Alzheimer’s Research UK, said in written comments.
“While research on the effect of vaccines on dementia risk continues, people should be aware that there are other factors that have been definitively linked to an increased risk of dementia. These include factors such as smoking, high blood pressure and excessive alcohol consumption,” Scales added. And controlling these factors can also make a difference to brain health.
A second study, to be presented Tuesday at the Alzheimer’s Association’s international conference, uses a similar approach to the Oxford study, and its findings mirror those results.
The study was funded by GSK, which issued a press release describing the results. The full study has not yet been peer-reviewed or published in a medical journal.
This research also uses another large database of electronic medical records, owned by the health care company Optum.
Using data from nearly 600,000 patients, the researchers were able to compare the diagnosis of dementia in people aged 50 and over who were vaccinated against shingles – with the older Zostavax vaccine or the newer Shingrix vaccine – with those who were vaccinated with Pneumovax, which protects against bacterial infections that cause strep throat and pneumonia.
After shingles vaccination, people in the study were less likely to be diagnosed with dementia than those who received the Pneumovax vaccine alone.
Get the weekly CNN Health newsletter
After five years, people who received the Zostavax vaccine were 8% less likely to be diagnosed with dementia and those who received the Shingrix vaccine were about 20% less likely to have a dementia diagnosis in their medical records compared with people who received the Pneumovax vaccine alone. This finding suggests that protection against the shingles virus is responsible for the difference, rather than vaccination alone or the healthy user effect.
The study also found that the new shingles vaccine was associated with a higher level of effectiveness than the old one. People who received the Shingrix vaccine were about 23% less likely after five years to be diagnosed with dementia compared with people who received the Zostavax vaccine.
Although the results are intriguing, the association needs to be studied further before researchers can know for sure that the shingles vaccine is definitively causing this benefit.
“The data at this point are an indication for further study, rather than a signal that we should change the way we use the vaccine,” said Dr Phil Dormitzer, who leads vaccine research and development for GSK.
For now, the best reason to get the shingles vaccine is to avoid the discomfort of shingles.