DEAR DR. ROACH: I recently read this morning that the shingles vaccine, Shingrix, “may have a protective effect against dementia.” It goes on to say the studies that have been conducted so far are only observational. Is this something that you could address? — J.S.B. ANSWER: There have been several studies showing that people who get a shingles vaccine (either the old one, Zostavax, which is no longer given, or the current vaccine, Shingrix, which provides longer-lasting benefit) are at a lower risk for developing dementia. However, in these kinds of studies, sometimes the people who get the vaccine are generally healthier and less likely to develop dementia anyway, so it’s impossible to be 100% sure that the vaccine is actually lowering the risk of dementia.
In the recent study that the news article was referring to, a change in the recommendations of who should get the shingles vaccine in the United Kingdom led to a large group of people being recommended the vaccine, while another large group of people who were almost the same age weren’t recommended the vaccine. In this way, the study was much closer to a randomized trial, which provides the highest degree of the evidence of a benefit.
In this study, those who had the Zostavax vaccine had a 3.5% point reduction in a new dementia diagnosis over seven years, which is equivalent to a 20% relative reduction in risk. The Shingrix vaccine would be expected to have an even greater benefit.
It has long been known that shingles increases the risk of stroke. Inflammation in the brain and blood vessels are suspected to cause the roughly double risk of stroke that is seen shortly after an episode of shingles. The increased risk for stroke goes down with time but is still present even a year after shingles.
Multiple stroke episodes are a leading cause of dementia, so it is biologically plausible that preventing shingles can reduce dementia by preventing blood vessel damage and strokes, although there may be other mechanisms at work.
Not getting painful shingles and its complication, post-herpetic neuralgia, is a good enough reason to recommend the shingles vaccine, but this new information makes getting the vaccine more important for adults over 50, even if they’ve had shingles or the old Zostavax vaccine.
