Residents of Wales born on either side of the cut-off date were analyzed based on their usage of preventive health services, previous diagnoses, and education level. The occurrence of dementia was compared among individuals on both sides of September 2, 1933. Initially, researchers validated that the vaccine effectively lowered the incidence of shingles, yielding results comparable to those in its clinical trials.
Overall, eligibility for the vaccine correlated with a 1.3 percent decline in the absolute risk of dementia diagnosis. This equates to an 8.5 percent reduction in relative risk; when adjusted for the fact that less than half of those eligible received the vaccine, this results in a 20 percent reduction in relative risk, which is quite significant.
To ensure the validity of their findings, researchers conducted the analysis again using a difference-in-difference method, arriving at nearly the same figures. This also rules out the chance that individuals seeking health care (for shingles or other conditions) were more likely to unintentionally receive a dementia diagnosis. They additionally compared the populations before and after in terms of various common health outcomes and found no changes between the two groups. Furthermore, no other aspects of NHS policy were altered with respect to the September 2 date.
Additionally, in a draft manuscript shared on Med arXiv, researchers observed a similar effect when analyzing UK HNS data to explore the shingles vaccines’ protective benefit regarding deaths attributed to dementia. Hence, all evidence suggests that the effect was genuine.
What’s occurring?
The researchers propose three possible explanations. One is straightforward: Reducing the reactivation of the varicella zoster virus delays dementia onset. However, it might also be that the effect is indirect—linking dementia to immune function, which the vaccine may influence. Lastly, there’s a chance that treatment for shingles could trigger the onset of dementia or heighten the rate of diagnoses.
