How did a shingles vaccine surprise researchers with a completely unrelated benefit?

The answer

A landmark real-world experiment in Wales provided the strongest evidence yet that the shingles vaccine could lower the risk of Alzheimer's disease and other forms of dementia. People who received the Shingrix vaccine were 20% less likely to develop dementia over the next seven years compared to those who didn't. A separate study found the vaccine slowed cognitive decline by 29.5% in those already diagnosed. Researchers believe the varicella-zoster virus may contribute to neuroinflammation, and the vaccine's immune response helps protect neural tissue - an entirely unintended benefit of a shot designed to prevent a painful skin rash.