Having shingles is no picnic. Patients have described the blistering sores and rash as being so painful as to make even a gentle touch a terrible ordeal.

It’s why medical guidelines suggest adults 50 and older get the two-dose shingles vaccine.

A new Stanford University study offers another good reason: It might help prevent dementia. Earlier, the researchers found that the vaccine might slow dementia’s progress.

The study came about because of how Wales rolled out the country’s national shingles vaccination program in 2013. It was set up so that anyone could receive the vaccine during the year they reached age 80.

But anyone who was already 80 or older when the program began was precluded from receiving the vaccine. That gave the Stanford scientists a natural experiment based on a large group of subjects they could track over time.

By 2020, when those who had not gotten the vaccine were about 86 years old, one in eight had developed dementia. Among those who received the shingles vaccine, the number was 20% lower.

And nearly half of the more than 7,000 Welsh seniors who had dementia when the program began died from dementia during follow-up. Of those with dementia who got the vaccine, only about 30% died from the disease.

Dementia affects more than 55 million people worldwide. Shingles is a viral disease, triggered by the same virus that leads to chickenpox, called varicella-zoster [vair-eh-sella zoss-ter]. The virus never fully leaves the body and can cause shingles later in life.

The results support an emerging idea among scientists that some viruses that affect the nervous system might increase the chance of developing dementia.