New results from a large study based on a ‘natural experiment’ in Wales confirm that vaccination against shingles can lower incidence of cognitive impairment and dementia and can also help slow progression of the disease.
The experiment involved 304,940 individuals born between 1925 and 1942. Those turning 80 immediately before September 2, 1933 were ineligible for shingles (herpes zoster) vaccination, whereas individuals who were 80 by this date could have the vaccination creating a sort of natural randomization process a bit like that seen in a clinical trial.
Earlier this year, lead investigator on the current study Pascal Geldsetzer, MD, PhD, an assistant professor at Stanford Medicine, and colleagues published research from the same group of people in Wales showing that having a shingles vaccination seemed to reduce the risk for developing dementia in older individuals.
The current study, published in Cell, expands on the original results and shows vaccination could also benefit individuals already diagnosed with dementia by slowing progression of their condition.
The study used Welsh electronic health records from the SAIL databank, covering about 80% of primary care practices, and linked with hospital and death certificate data. Of the more than 300,000 people included in the study, 282,557 had no prior cognitive impairment and 14,350 had a dementia diagnosis prior to September 2013.
The age of the group ranged from 71–88 years, with the group nearest to age 80 being the most relevant for the ‘natural’ randomization that occurred.
“What makes the study so powerful is that it’s essentially like a randomized trial with a control group—those a little bit too old to be eligible for the vaccine—and an intervention group—those just young enough to be eligible,” Geldsetzer said in a press statement.
The current study showed eligibility for vaccination cut the nine‑year incidence of mild cognitive impairment by 1.5 percentage points and this figure was higher, at 3.1 percentage points, if people were actually vaccinated.
In those who already had dementia at enrollment, being eligible for vaccination reduced deaths from dementia over nine years of follow up by 8.5 percentage points and by 29.5 percentage points in those actually vaccinated. Similar reductions were seen for all-cause mortality. Notably, this effect on mortality was not seen in those without dementia.
“The most exciting part is that this really suggests the shingles vaccine doesn’t have only preventive, delaying benefits for dementia, but also therapeutic potential for those who already have dementia,” Geldsetzer said.
Vaccination seemed to benefit women to a much greater extent than men, both for reducing incidence of cognitive impairment and mortality in those with dementia over the follow up period.
The reasons for the sex-specific effect are not totally clear, but research suggests that women’s immune systems both respond more strongly to the shingles vaccine and are more vulnerable to the dementia‑relevant consequences of an outbreak of herpes zoster, so this could explain the added benefit women seem to gain from the vaccination.
