https://www.npr.org/sections/health-shots/2020/07/27/894731147/flu-shot-and-pneumonia-vaccine-might-reduce-alzheimers-risk-research-shows


I certainly hope this may be true, since my father's side of the family had a history of early onset Alzheimers.  One of my great-aunts couldn't recognize her own children while she was in her 50's.  My dad started showing signs in his 60s, we had to put him in a home when he was my age.  My mother died of cancer.  My father of Alzheimers and accumulated small strokes.  Of the two, at least my mother was still the person I knew until her death.  Dad was just a lost soul occupying his body.  
As per your comments about bee stings, COVID, and statistics, I agree with your assessment of the complexities and the statistical challenges.
My example of the power of big data statistics - the poultry industry years ago found that feeding turkeys a small amount of arsenic increased the rate of weight gain.  But no small farm or backyard gardener with chickens or turkey would ever notice the difference.  If was small, but enough that the large, corporate companies, with tens of thousands of turkeys could see the difference.
Jerry
P.S.  This is also why FDA, at least at one time, required turkeys to be tested and set allowable levels of arsenic.  Think about that next Thanksgiving.
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