People with dementia who received a shingles vaccine were significantly less likely to die from dementia than those who didn't get the shot, according to findings of a large study, suggesting the vaccine could slow progression of the disease.
Overall, nearly half of the more than 14,000 seniors in Wales who had dementia at the start of the vaccination program died from dementia during nine years of follow-up.
But receipt of Merck's Zostavax vaccine lowered the risk of death from dementia by nearly 30 percentage points, researchers reported in Cell.
Earlier this year, researchers in Wales had found that older adults who received the Zostavax vaccine were 20% less likely to develop dementia in the first place, compared to similar seniors who did not receive the vaccine.
"The most exciting part (of the newer findings) 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," study leader Dr. Pascal Geldsetzer of Stanford University in California said in a statement.
Whether the shingles vaccine protects against dementia by revving up the immune system overall, by specifically reducing reactivations of the virus that causes shingles, or by some other mechanism is still unknown, the researchers said.
Also unknown is whether the newer shingles vaccine, Shingrix from GlaxoSmithKline, which contains only certain proteins from the virus and is more effective at preventing shingles, may have a similar or even greater impact on dementia than the older vaccine received by participants in the Wales studies.
Protection against shingles with Merck's vaccine was found to wane over time and it is no longer used in most countries after Shingrix was shown to be superior.
The researchers say that in the past two years, they have replicated the Wales findings in health records from other countries, including England, Australia, New Zealand and Canada.
"We just keep seeing this strong protective signal for dementia in dataset after dataset," Geldsetzer said.
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