In 2013 in Can the Shingles Vaccine Prevent Dementia? I wrote:

A new paper provides good evidence that the shingles vaccine can prevent dementia, which strongly suggests that some forms of dementia are caused by the varicella zoster virus (VZV), the virus that on initial infection causes chickenpox.

We now have three studies–from America, Australia and Canada–that find similar results using large numbers and credible research designs. Thus, I think we can up this to the Shingles vaccine reduces dementia.

Eric Topol summarizes the new evidence and writes:

If you are 50+ and have not gotten Shingrix vaccinated, you may want to consider that. You get protection vs Shingles (which can be dreadful), slowing of your biological aging (by methylation and RNA metrics), and ~20% reduction of dementia, predominantly related to Alzheimer’s disease. All of this benefit is magnified in women compared with men, but 3 of the studies showed some reduction of dementia in men. As a tradeoff, men appear to derive more cardiovascular benefit, but that evidence is not as compelling as protection from dementia from natural experiments.