Research using the introduction of the shingles vaccine in Wales has shown that vaccination can significantly reduce the risk of dementia in the elderly. The study analyzed data from more than 280,000 people and found that those vaccinated had a 20% lower risk of developing dementia during follow-up. The protective effect was observed even after multiple analyses, and was stronger in women. The results suggest that the vaccine may have a protective effect even in people who already suffer from dementia, suggesting a possible therapeutic effect. The study used a natural experiment thanks to age-specific vaccination rules. Most of the data come from retrospective observational studies that show association, not causation. The results are supported by other studies and meta-analyses, which report a 20-35% reduction in the risk of dementia. Randomized clinical trials are underway to confirm these results.