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, 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.

“All these associational studies suffer from the basic problem that people who get vaccinated have different health behaviors than those who don’t,” said Pascal Geldsetzer, MD, PhD, assistant professor of medicine, an affiliated faculty member at Stanford Health Policy, and senior author of the new study. “In general, they’re seen as not being solid enough evidence to make any recommendations on.”

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.

Read the Full Story by Nina Bai at Stanford Medicine News Center