Reacción a "Reactions: pre-publication claims part of dementia cases are caused by herpes-like viruses"

It is a good quality study. It provides stronger evidence that Zostavax, a herpes zoster vaccine, reduces the risk of dementia. The study, however, didn’t prove that the effect of the vaccine is mediate by its effect on the herpes zoster virus.  

Further, Zostavax is being replaced by a newer vaccine (Shingrix). Shingrix is more potent than Zostavax against shingles, so we can hope that it is at least as effective as Zostavax to prevent dementia, but we do not really know, because none of the participants in the study was administered Shingrix. 

The study is rigorous, and I believe its main results are valid, but chance remains a possible explanation. The p-value, which is a measure of how frequently results as strong as those reported could occur by chance alone, was in a range traditionally described as “significant”, but not low enough to confidently exclude chance as a possible explanation.