Can the shingles vaccine ward of dementia?

Previous studies based on health records have linked the shingles vaccine with lower dementia rates, but they could not account for a major source of bias: People who are vaccinated also tend to be more health conscious in myriad, difficult-to-measure ways. Behaviors such as diet and exercise, for instance, are known to influence dementia rates, but are not included in health records.

“All these associational studies suffer from the basic problem that people who get vaccinated have different health behaviors than those who don’t,” said Pascal Geldsetzer, MD, PhD, assistant professor of medicine and senior author of the new study. “In general, they’re seen as not being solid enough evidence to make any recommendations on.”

Dementia affects more than 55 million people worldwide, with an estimated 10 million new cases every year. Decades of dementia research has largely focused on the accumulation of plaques and tangles in the brains of people with Alzheimer’s, the most common form of dementia. But with no breakthroughs in prevention or treatment, some researchers are exploring other avenues — including the role of certain viral infections.

Shingles, a viral infection that produces a painful rash, is caused by the same virus that causes chicken pox — varicella-zoster. After people contract chicken pox, usually in childhood, the virus stays dormant in the nerve cells for life. In people who are older or have weakened immune systems, the dormant virus can reactivate and cause shingles.

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Two years ago Geldsetzer recognized a fortuitous “natural experiment” in the rollout of the shingles vaccine in Wales that seemed to sidestep the bias. The vaccine used at that time contained a live-attenuated, or weakened, form of the virus.

The vaccination program, which began Sept. 1, 2013, specified that anyone who was 79 on that date was eligible for the vaccine for one year. (People who were 78 would become eligible the next year for one year, and so on.) People who were 80 or older on Sept. 1, 2013, were out of luck — they would never become eligible for the vaccine.

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. By 2020, one in eight older adults, who were by then 86 and 87, had been diagnosed with dementia.

But those who received the shingles vaccine were 20% less likely to develop dementia than the unvaccinated. “It was a really striking finding,” Geldsetzer said. “This huge protective signal was there, any which way you looked at the data.” Future studies will be needed to figure out how to develop a vaccine and this may take years. We aren’t going to push vaccines on anyone, but this might convince some people to take the shingles vaccine as a precaution. Also, there are 5 times more microplastics found in the brains of people with dementia. Finding ways such as sauna treatments might help us sweat those plastics out of the system.