Older adults who received the Shingrix shingles vaccine were 24% less likely to be diagnosed with dementia over four years in a study of more than 500,000 people. Researchers estimate the difference could amount to roughly one dementia case prevented for every 17 people vaccinated.
This is why these studies have to be done in non-shitholes that have universal health care.
https://www.nature.com/articles/s41586-025-08800-x
Due to a bureaucratic decision, people in UK got Shingrex, or not, born one week apart. People with vaccine, 20% less Alzheimer. But, the effect was only seen in woman.