This study used the national rollout of the vaccine in Wales so they had closer to randomized trials without doing randomized trials if that makes sense. In the USA (where a lot of prior data came from) people who got the vaccine may not represent that sort of data due to insurance and vaccine hesitancy.
Related:
Evidence mounts that shingles vaccines protect against dementia (42 points, 8 months ago, 14 comments) https://news.ycombinator.com/item?id=36083620
This study used the national rollout of the vaccine in Wales so they had closer to randomized trials without doing randomized trials if that makes sense. In the USA (where a lot of prior data came from) people who got the vaccine may not represent that sort of data due to insurance and vaccine hesitancy.
https://www.nature.com/articles/s41586-025-08800-x