If you study effects and not causes due to lack of measurements for reproducibility in any field of research, that's what comes out.
Also check out how the new and promising correlation started by observing the Wales eligibility for mandatory shingles vaccination during an outbreak and the effect on that test group when it comes to alzheimer or dementia in their old age.
Note that shingles (herpes zoster) virus is a dormant virus for decades, and it's not really treated because of that.
Also note that this was only discovered because people died and their data set was publicized because of that, which I hope that can happen in an anonymous way due to it being invaluable for medical research.
[1] https://www.alzheimer-europe.org/news/analysis-electronic-he...
[2] https://pmc.ncbi.nlm.nih.gov/articles/PMC11485228/
[3] https://www.sciencedirect.com/science/article/pii/S009286742...
[4] https://www.alzforum.org/news/research-news/shingles-vaccine...