An older shingles vaccine may offer unexpected protection against dementia, new research suggests.

A recent study published in Nature found that people who received Zostavax, a shingles vaccine that’s no longer in use in the United States, had a lower risk of developing dementia.

Based on over 280,000 health records of older adults, those who received Zostavax were 20% less likely to develop dementia in the seven years following the vaccination than those who did not.

The findings add to growing evidence that vaccines may play a role in reducing the risk of neurodegenerative diseases.

Shingles is a painful rash illness caused by the reactivation of the varicella zoster virus, the same virus that causes chickenpox. After a person recovers from chickenpox, the virus can remain dormant in nerve cells and reactivate later in life.

Zostavax is a live attenuated vaccine that uses a weakened form of the virus. This type of vaccine was not recommended for people with weakened immune systems, as it could occasionally trigger shingles in those individuals.

Zostavax was discontinued in the U.S. in 2020. Shingrix, a more effective and safer option, had been approved in 2017. Shingrix is given as a two-dose series and rarely causes infections from the virus.

Shingles Vaccine Helps Cut Dementia Risk

The Nature study isn’t the first to show a connection between a shingles vaccine and a lower risk of dementia. Last year, another study by Oxford researchers found an even stronger association between Shingrix and dementia protection.

The study also showed that protection against dementia was stronger in women, which could be due to sex differences in immune response or in the way dementia develops, the authors wrote.

People who are vaccinated also tend to live healthier lives, including having better diets and more exercise, which can also protect against dementia, said Pascal Geldsetzer, MD, PhD, senior author of the new study and an assistant professor of medicine at the Stanford University School of Medicine.

Geldsetzer said that lifestyle information was generally absent from patient health records, so it was difficult to determine if lifestyle factors contributed to dementia risk in previous research.

However, the study was sparked by a unique circumstance in Wales. Starting Sep. 1, 2013, people who were exactly 79 years old became eligible to receive Zostavax for one year. After that, eligibility shifted to the next group of 79-year-olds. Those who were 80 or older as of that date were never eligible.

Researchers emphasized data from people who made the cutoff date by a week and those who turned 80 a week before the rollout. They accounted for potential differences between the vaccinated and unvaccinated groups, such as medication use and doctor visits. After weeding out those factors, the vaccinated group was 20% less likely to be diagnosed with dementia.

Why Shingles Vaccine Helps Cut Dementia Risk

There are two potential explanations for why the shingles vaccine can protect against dementia.

For one, Geldsetzer said, emerging research shows that the varicella zoster virus that hibernates in the nervous system could contribute to the development of dementia.

Another theory is that vaccines in general may have a neuroprotective effect. Prior research showed that vaccines against influenza and pneumonia were also linked to a lower risk of Alzheimer’s dementia.

“There is increasing evidence showing that vaccines can have effects on the immune system that are broader than just eliciting the specific antibody response for which they have been designed, and that these broader immunological effects can have benefits for other diseases,” Geldsetzer said.

Yet Another Reason to Get the Shingles Vaccine

While the new study isn’t enough to prove that the shingles vaccine can reduce the risk of dementia, it may offer yet another reason for older adults to get vaccinated, said William Schaffner, MD, a spokesperson for the Infectious Diseases Society of America and an infectious disease specialist at Vanderbilt University.

“Doctors can say to patients if you need one other reason to push you to get Shingrix sooner than later or at all, there are a constellation of studies—none of them by themselves definitive—that suggest the vaccine could be protective against dementia,” Schaffner said.

About one in three people in the U.S. will develop shingles in their lifetime, and the risk increases with age. However, only a third of eligible U.S. adults received at least one dose of the shingles vaccine in 2021, according to data from the Centers for Disease Control and Prevention (CDC).

The bottom line is to get vaccinated against shingles, said Preeti Malani, MD, an infectious disease specialist at Michigan Medicine. “Decreasing the risk of dementia might be a bonus, but the vaccine definitely decreases the risk of shingles, which is more than enough reason to get vaccinated,” Malani added.

The CDC advises everyone 50 and older to get two doses of the Shingrix vaccine. Shingles can cause years of severe pain in some people who contract the virus and even blindness if the shingles rash appears on the face.