New study suggests shingles vaccine may reduce or delay dementia risk

A new study by researchers at Stanford University and McMaster University in Hamilton, Canada, has found evidence that live attenuated herpes zoster (shingles) vaccination prevents or delays dementia onset.

The study, published in The Lancet in February, analyzed the effects of eligibility for the shingles vaccination on later dementia diagnoses in older adults in Canada.

“For the first time, we now have evidence that likely shows a cause-and-effect relationship between shingles vaccination and dementia prevention,” Pascal Geldsetzer, M.D., Ph.D., M.P.H., assistant professor of medicine of epidemiology and population health at Stanford University, told MHE. “We find these protective effects to be large in size — substantially larger than those of existing pharmacological tools for dementia.”

The findings reported by Geldsetzer and his colleagues are among the latest in a series pointing to the shingles vaccine having beneficial effects beyond preventing the reactivation of the chicken pox virus causes shingles.

Related: Shingles — but also RSV — vaccination associated with lower dementia risk

Leveraging a natural experiment created by a policy change in Ontario’s vaccine program, the researchers compared individuals born just before and just after the eligibility cutoff for a publicly funded live attenuated shingles vaccine. Over nearly 5½ years of follow-up, being eligible for and receiving the shingles vaccine was associated with about a 2% lower incidence of dementia diagnoses and evidence of a modest delay in disease onset compared with those who were slightly younger and ineligible under the program’s rules.

Geldsetzer, who served as lead author on the study, noted there are two broad mechanisms that link dementia and shingles vaccination, and they are not mutually exclusive.

“The first mechanism is specific to the chickenpox virus,” he said. “There is a growing body of research showing that viruses that preferentially target your nervous system and hibernate in your nervous system for much of your life may be implicated in the development of dementia. One such virus, of course, is the chickenpox virus, which can cause shingles later in life.”

The second mechanism, he noted, is potentially independent of the chickenpox virus.

“Specifically, there is increasing evidence showing that vaccines can have effects on the immune system that are broader than just eliciting the specific antibody response for which they have been designed, and that these broader immunological effects can have benefits for other diseases,” he said.

Although there have been many analyses in electronic health record and medical claims data that have found that receiving a given vaccine is correlated with a reduced risk of dementia in the future, the majority of those studies have all compared those who go get vaccinated with those who do not.

“The critical limitation of this research is that we know that the health behaviors of those who get vaccinated are different to those who do not, and we have very little, if any, information on these behaviors in electronic health record or medical claims data,” Geldsetzer said. “We, for instance, do not know about dietary behaviors or physical activity levels. We, therefore, don't know if we're merely looking at correlations or actual cause and effect.”

This study, he continued, takes a fundamentally different approach and, thus, provides a very different level of evidence.

A previous study by the researchers published in Nature last examined a cohort of patients in Wales.

“What’s so special about our study is that we take advantage of a very similar scenario to a randomized trial,” Geldsetzer said. “In Wales, when they rolled out the shingles vaccine back in 2013, they said that if you had your 80th birthday just prior to the start date of the program, you are ineligible and you remain ineligible for life. While if you had your 80th birthday just after, you were eligible for at least one year. We see in our data, that just a one-week difference across this date-of-birth cutoff means that you go from essentially no one getting vaccinated to about half of the population getting vaccinated.”

In the current study, Geldsetzer and his team show that the same protective effect appears in Ontario.

“Ontario offers a unique opportunity to confirm our Wales findings because it used two different date of birth eligibility cutoffs,” he said. “In addition, the fact that only Ontario rolled out a publicly funded shingles vaccine program, it allows for a comparison between Ontario and other Canadian provinces. As in Wales, we find large protective effects for dementia at both date of birth eligibility cutoffs in Ontario, and we do not see these effects in Canadian provinces that did not have a shingles vaccination program.”

Geldsetzer is currently trying to raise funds for a new trial to definitively test if shingles vaccination prevents or delays dementia.