- A vaccination policy in Wales created a natural experiment to see the impact of the shingles vaccine on dementia.
- A Stanford study suggests the shingles vaccination lowers risk of developing dementia by 20%.
- More than 55 million people worldwide have some form of dementia and 10 million cases are added each year.
The shingles vaccine may reduce the risk of developing dementia over seven years by about 20%. That’s more than any other known intervention, according to research from Stanford.
The findings are based on what the Stanford news service calls “an unusual public health policy in Wales,” which created what amounts to a natural experiment. The Stanford Medicine study findings were published this month in the journal Nature. “If further confirmed, the new findings suggest that a preventive intervention for dementia is already close at hand,” the researchers said in a news release.
About shingles
After someone gets chicken pox, the varicella-zoster virus stays dormant in the nerve cells for the rest of the person’s life. If the immune system gets weak or the person becomes frail, the virus can reawaken and cause the painful rash that is shingles.
The herpes zoster vaccine is designed to reduce risk of developing shingles among older adults.
About dementia
More than 55 million people worldwide have some form of dementia and another 10 million cases are added each year. While the release noted that most of the research has focused on the plaques and tangles in the brain that are a hallmark of Alzheimer’s disease, scientists have been exploring the role of certain viral infections in the development of dementia, too.
Some of that research has suggested that the vaccine designed to tame the varicella-zoster’s reemergence could result in less dementia, but it’s been very hard to quantify and prove. And it’s possible, as well, that folks who keep up on vaccinations are doing other healthy things that improve their odds of protecting their brain.
A natural experiment
The Wales vaccination policy that was introduced in 2013 may have changed that calculation a bit.
Under the policy, anyone age 79 was eligible for the vaccine for one year. As people in subsequent years turned 79, they too would be eligible for a year. Those who were 80 or older would not be eligible at all.
According to the Stanford article, “These rules, designed to ration the limited supply of the vaccine, also meant that the slight difference in age between 79- and 80-year-olds made all the difference in who had access to the vaccine. By comparing people who turned 80 just before Sept. 1, 2013, with people who turned 80 just after, the researchers could isolate the effect of being eligible for the vaccine.”
That came pretty close to creating a randomized controlled trial, said Dr. Pascal Geldsetzer, assistant professor of medicine and senior author of the new study.
Analyzing the data
The Stanford team looked at the records of 280,000 older adults ages 71-88 who didn’t have dementia when the vaccination program began, comparing those who turned 80 the week before to those who hit the milestone the week after the program began.
Besides the tiny difference in age, a thousand people in each group should otherwise be pretty similar, on average, Geldsetzer said.
For seven years, they followed the health outcomes of the two groups. And when they considered actual vaccination rates, they could see the vaccine’s impact.
By 2020, 1 in 8 older adults, then either age 86 or 87, had been diagnosed with dementia. But the group that was vaccinated was 20% less likely to develop the neurocognitive decline than those who were not vaccinated.
The researchers looked closely for other variables that might account for the difference, but found the two groups “to be indistinguishable in all characteristics” save shingles vaccine status. They were similar in terms of education, for instance. They had similar other health issues, too. But the vaccinated group had fewer dementia diagnoses.
The protective effect was stronger for women than for men, per the study.
What researchers don’t know is why the vaccine appears to be somewhat protective. They wondered if it boosted the immune system, but they don’t know. They also wonder if a new version of the vaccine “which contains only certain proteins from the virus and is more effective at preventing shingles, may have a similar or even greater impact on dementia.”
While they hope to create their own large, randomized controlled trial, they’ve spent two years replicating the Wales findings in health records from Australia, Canada, England and New Zealand.
“We just keep seeing this strong protective signal for dementia in dataset after dataset,” Geldsetzer said in the release.
Besides the Stanford team, a researcher from the Vienna University of Economics and Business contributed to the study.