Flu vaccination linked to 40% reduced risk of Alzheimer’s disease

That's an incredible effect size.

Mechanisms hypothesized to be at play:

"These mechanisms—and those underlying the effects of adulthood vaccinations on all-cause dementia risk in general—can be grouped into at least three broad, non-exclusive categories: 1) influenza-specific mechanisms, including mitigation of damage secondary to influenza infection and/or epitopic similarity between influenza proteins and AD pathology; 2) non–influenza-specific training of the innate immune system; and 3) non–influenza-specific changes in adaptive immunity via lymphocyte-mediated cross-reactivity."

Purely anecdotal; I found it odd to see my mother (diagnosed with alzheimer 3/4 year ago) behaving and talking more coherent days after her mRNA covid-19 vaccine shots. I thought perhaps the immune response lessened the symptoms temporarily.

Whether or not that's an incredible effect size sort of depends. For infectious disease epidemiology, which regularly sees extremely strong effects because of the very short causal chain between an infection and an outcome, it's not all that extraordinary.

It is an effect size that commands legitimate and substantial attention.

It indicts everyone still huddled around the amyloid lamppost.

Agreed. I've just also seen "That's a huge effect size" as a way to dismiss observational results as probably wrong, and so felt it should be noted that for things with infectious etiologies this is impressive but not particularly outlandish (vs. say environmental epidemiology, where an effect size of this magnitude would mean congressional hearings).