Comparing Outcomes in Older Adults
Dr. Geldsetzer and his collaborators were able to compare two groups of older adults who had nearly identical characteristics other than vaccination status because of an immunization program in Wales that began on September 1, 2013.
Under the program, which was designed to ration vaccine supply, anyone who was age 79 on that date was eligible for the vaccine for one year. People who were 80 or older on that date were out of luck — they would never become eligible. (As more people reached age 79 in the years to come, they would become eligible until they turned 80.)
The investigative team reviewed health records of over 280,000 individuals between ages 71 and 88 who did not have dementia at the start of the vaccination program. They focused their analysis, however, on those closest to either side of the eligibility threshold — comparing people who turned 80 in the week before September 1, 2013, with those who turned 80 in the week after.
The study took into account confounding factors that might have influenced dementia risk, such as use of preventive health services, past common disease diagnoses, and educational attainment. The scientists found the two groups to be indistinguishable in all characteristics.
“So, this is just like a randomized trial,” says Geldsetzer. “We have a vaccine-eligible and a vaccine-ineligible group for which we know that they should be on average similar to each other, and therefore good comparison groups, because all that’s different about these two groups is if they were born a few days earlier or a few days later.”
Furthermore, the researchers noted that the effect of vaccination on dementia risk was much more pronounced in women than men.
“This could potentially be due to sex differences in the immune response or in the way in which dementia develops,” says Geldsetzer. “Women on average have higher antibody responses to vaccination, for example. We also know that both shingles and dementia are more common in women than in men.”
What Causes Shingles?
Shingrix vs. Zostavax
The only brand of shingles vaccine currently available in the United States is Shingrix. The vaccine used during this study was an older shot, Zostavax, that is no longer in use in the United States, points out Robert H. Hopkins Jr., MD, medical director of the National Foundation for Infectious Diseases (NFID).
As to why the shot may have this positive effect on brain health, Hopkins speculates that immune system stimulation may be a factor, adding that more research is needed to explore this potential benefit.
“Shingles can have a devastating impact on a person’s health and quality of life,” he says. “ If the shingles vaccine also reduces the risk of dementia, that is one more important benefit that may improve the quality of life of many older persons.”
