People are always looking for ways to lower their risk of dementia in their senior years. For a while now there has been research suggesting that older adults getting vaccines (e.g., annual flu shots) lower their risk of dementia and Alzheimer's disease. A recent study found that the shingles vaccine (herpes zoster vaccine) has a similar protective effect.
Adults in their 70s who received the shingles vaccine had a lower incidence of dementia. They were 20% less likely to develop dementia over the next 7 years. And the differences in rate of dementia among those who received or didn't receive the vaccine started within 1 1/2 years of getting the vaccine.
The study also showed that the protection against dementia was stronger in women than in men - that is, the shingles vaccine benefited women more than men.
By the way, one could view lower incidence of dementia as a non-target effect. The target was shingles, but other protective health effects are non-target effects.
Excerpts from Science Daily: Study strengthens link between shingles vaccine and lower dementia risk
An unusual public health policy in Wales may have produced the strongest evidence yet that a vaccine can reduce the risk of dementia. In a new study led by Stanford Medicine, researchers analyzing the health records of Welsh older adults discovered that those who received the shingles vaccine were 20% less likely to develop dementia over the next seven years than those who did not receive the vaccine.
The remarkable findings, to be published April 2 in Nature, support an emerging theory that viruses that affect the nervous system can increase the risk of dementia. If further confirmed, the new findings suggest that a preventive intervention for dementia is already close at hand.
Shingles, a viral infection that produces a painful rash, is caused by the same virus that causes chicken pox -- varicella-zoster. After people contract chicken pox, usually in childhood, the virus stays dormant in the nerve cells for life. In people who are older or have weakened immune systems, the dormant virus can reactivate and cause shingles.
Dementia affects more than 55 million people worldwide, with an estimated 10 million new cases every year. Decades of dementia research has largely focused on the accumulation of plaques and tangles in the brains of people with Alzheimer's, the most common form of dementia. But with no breakthroughs in prevention or treatment, some researchers are exploring other avenues -- including the role of certain viral infections.
Previous studies based on health records have linked the shingles vaccine with lower dementia rates, but they could not account for a major source of bias: People who are vaccinated also tend to be more health conscious in myriad, difficult-to-measure ways. Behaviors such as diet and exercise, for instance, are known to influence dementia rates, but are not included in health records.
But two years ago, Geldsetzer recognized a fortuitous "natural experiment" in the rollout of the shingles vaccine in Wales that seemed to sidestep the bias. The vaccine used at that time contained a live-attenuated, or weakened, form of the virus.
The vaccination program, which began Sept. 1, 2013, specified that anyone who was 79 on that date was eligible for the vaccine for one year. (People who were 78 would become eligible the next year for one year, and so on.) People who were 80 or older on Sept. 1, 2013, were out of luck -- they would never become eligible for the vaccine.
These rules, designed to ration the limited supply of the vaccine, also meant that the slight difference in age between 79- and 80-year-olds made all the difference in who had access to the vaccine. By comparing people who turned 80 just before Sept. 1, 2013, with people who turned 80 just after, the researchers could isolate the effect of being eligible for the vaccine.
The circumstances, well-documented in the country's health records, were about as close to a randomized controlled trial as you could get without conducting one, Geldsetzer said.
The researchers looked at the health records of more than 280,000 older adults who were 71 to 88 years old and did not have dementia at the start of the vaccination program. They focused their analysis on those closest to either side of the eligibility threshold -- comparing people who turned 80 in the week before with those who turned 80 in the week after.
Protection against dementia
As expected, the vaccine reduced the occurrence over that seven-year period of shingles by about 37% for people who received the vaccine, similar to what had been found in clinical trials of the vaccine. (The live-attenuated vaccine's effectiveness wanes over time.)
By 2020, one in eight older adults, who were by then 86 and 87, had been diagnosed with dementia. But those who received the shingles vaccine were 20% less likely to develop dementia than the unvaccinated.
"It was a really striking finding," Geldsetzer said. "This huge protective signal was there, any which way you looked at the data.".... The only difference was the drop in dementia diagnoses.
Nevertheless, his team analyzed the data in alternate ways -- using different age ranges or looking only at deaths attributed to dementia, for example -- but the link between vaccination and lower dementia rates remained.
"The signal in our data was so strong, so clear and so persistent," he said.
In a further finding, the study showed that protection against dementia was much more pronounced in women than in men. This could be due to sex differences in immune response or in the way dementia develops, Geldsetzer said. Women on average have higher antibody responses to vaccination, for example, and shingles is more common in women than in men.
Whether the vaccine protects against dementia by revving up the immune system overall, by specifically reducing reactivations of the virus or by some other mechanism is still unknown.
Also unknown is whether a newer version of the vaccine, which contains only certain proteins from the virus and is more effective at preventing shingles, may have a similar or even greater impact on dementia.
In the past two years, his team has replicated the Wales findings in health records from other countries, including England, Australia, New Zealand and Canada, that had similar rollouts of the vaccine. "We just keep seeing this strong protective signal for dementia in dataset after dataset," he said.