by Charys D. Hong

A unique natural experiment in Wales has produced convincing evidence that the shingles vaccine can delay or prevent dementia. In a new study led by Stanford Medicine, researchers analyzing the medical records of Welsh older adults discovered that the risk of developing dementia over the next seven years was 20% lower among those who received the vaccine compared to those who did not receive the vaccine.

“It was a really striking finding,” Pascal Geldsetzer, MD, PhD, assistant professor of medicine at Stanford and senior author of the new study, told Stanford Medicine. “This huge protective signal was there, any which way you looked at the data.”

The findings,  published in Nature, build on earlier research that suggests that viral illnesses may increase the chances of developing neurodegenerative diseases. When the virus that causes shingles reactivates, it can travel to the brain where it may inflame and damage brain cells, including neurons responsible for reasoning, memory, and communication. The shingles vaccine is thought to prevent viral reactivation and reduce brain inflammation, helping to prevent cognitive decline. It may also trigger a broader immune system response other than the antibody response that supports overall brain health. 

The Stanford research team based their new findings on a fortuitous “natural experiment” in the rollout of the shingles vaccine in Wales. The vaccination program, which began Sept. 1, 2013, specified that anyone younger than 80 on the following day was eligible for the vaccine for one year. These rules, designed to ration the limited supply of the live-attenuated vaccine used at that time, meant that just a few weeks’ difference in birth dates determined who had access to the vaccine.

The researchers analyzed electronic health record data of more than 280,000

adults between the ages of 71 to 88 who did not have dementia at the start of the vaccination program. They focused their analysis on those closest to either side of the eligibility threshold — comparing people who turned 80 in the weeks before with those who turned 80 in the weeks after. By 2020, one in eight adults, who were by then 86 and 87 years old, had been diagnosed with dementia. But those who received the shingles vaccine had a 20% lower risk of developing dementia than the unvaccinated.

Further research is needed to establish whether Shingrix, the recombinant vaccine now used to prevent shingles, has comparable effects in preventing dementia as the live-attenuated vaccine used in the Wales experiment.  As research shifts from large-scale health databases to targeted randomized controlled trials, the case for a vaccine-based approach to preventing dementia is likely to become more clinically relevant in the near future.

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