Could the shingles vaccine lower your risk of dementia?

This might seem like a bizarre link, but research has previously shown an older version of the shingles vaccine, Zostavax, reduced the risk of dementia.

In this new study, published in the journal Nature Medicine, researchers found Shingrix delayed dementia onset by 17% compared with Zostavax.

So how did they researchers work this out, and how could a shingles vaccine affect dementia risk?