Results drawn from a “unique natural randomisation” show that patients that received the Zostavax vaccination for herpes zoster have the probability of a new dementia diagnosis reduced “by approximately one fifth over a seven-year follow-up period”, researchers said.
Patients that received the shingles vaccine had the probability of a new dementia diagnosis reduced by 3.5 percentage points over the seven-year follow-up period, the preprint paper published on medRxiv last week (May 25) found.
This corresponded to a 19.9% relative reduction in dementia when compared to people that did not receive the vaccine, it said.
Huge sample
The study – which is yet to be peer-reviewed – took “advantage” of the strict rules in Wales for Zostavax eligibility, which provides inoculation against shingles.
Researchers used “rich” countrywide data - a huge sample of 282,541 adults - to compare the dementia outcomes of people in Wales born before September 2 1933 and therefore ineligible to receive the vaccine with those born after that date, who could receive it.
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From September 2013 in Wales, 16,595 people born between September 2 1933 and September 1 1934 became eligible to receive the shingles vaccine, the paper said.
People born before this date could not receive the vaccine but people born after became eligible as time went on, according to strict date-of-birth rules, it added.
Just 0.01% of those who were “one week too old to be eligible” received Zostavax, compared to 47.2% of “those who were just one week younger”, according to the paper.
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The very close comparison between dates of birth meant that there should be “no plausible reason” for a systematic difference between the groups, except that the younger group could be vaccinated against shingles, according to the researchers.
They showed that there were no other “systematic differences” between these two groups - for instance, other interventions that used the same date cut-off, that receiving the shingles vaccine made a person more likely to receive other vaccines or that the vaccine had an effect on another cause of morbidity or mortality.
Vaccine “very likely” to prevent or delay dementia
This “unique quasi-experimental setting” meant that they could find the causal effect rather than just correlation of the shingles vaccine on dementia, they said.
The authors argued that shingles vaccination is “very likely” to be an effective way of “preventing or delaying” dementia.
They said that “arguably even more importantly”, their finding “could help elucidate the pathogenesis of dementia”, which could produce better treatments through understanding the process of its development.
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Zostavax is offered through GPs for free on the NHS for people aged 70 to 79. People with a weak immune system are offered a non-live alternative vaccine called Shingrix.
Community pharmacies can also offer shingles vaccines privately.
For instance, some branches of Kamsons Pharmacy offer shingles vaccines for patients over the age of 50 for £175. Some Boots branches also offer Shingrix for £450 for the same age cohort.
However, the study only considered Zostavox as Shingrix entered the UK market in 2021, after the end of the study’s follow-up period, it said.
