Comment by scythe

In short:

- Wales imposed an arbitrary hard cutoff (1933-9-2) on shingles vaccine, giving excellent randomization in a natural experiment

- Randomization confirmed by comparison of preëxisting conditions

- Individuals born after Sept 2, 1933 show a noticeable discontinuity in dementia diagnoses compared to those born prior to Sept 2, 1933, as seen in Figure 3

- Analysis indicates a 20% relative risk reduction across several types of dementia from receiving the VZ vaccine.

This is not like the EBV–MS connection: nothing in the stats so far suggests that varicella zoster is essential or nearly so to developing Alzheimer's disease or other dementia, but it is strong evidence that it contributes to the development of dementia.