The shingles vaccine also may offer protection against dementia, which affects nearly 7 million Americans, according to a new study.
The research, published Wednesday in the journal Nature, found vaccinated older adults were 20% less likely to develop dementia over the next seven years than their unvaccinated counterparts. Women were much more likely to benefit from the vaccine than men.
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If the findings bear out in future studies, a much-sought-after intervention for dementia, the most common form being Alzheimer's disease, could be accessible. Finding preventions for dementia has become more urgent as diagnoses continue to spike.
"If you're reducing the risk of dementia by 20%, that's quite important in a public health context, given that we don't really have much else at the moment that slows down the onset of dementia," Dr. Paul Harrison, a professor of psychiatry at the University of Oxford in England, told the New York Times.
Harrison did not conduct the study, but he has researched the link between the shingles vaccine and the reduced risk of dementia.
A study published in January showed that the risk of developing dementia was two times higher than noted in previous research, with Americans over 55 having a 42% risk of developing dementia at any time. That means new dementia cases in the United states are expected to double from about 500,000 in 2020 to more than 1 million in 2060. Worldwide, dementia cases are projected to double every 20 years, from more than 55 million in 2020 to 78 million in 2030 and 139 million in 2050, according to Alzheimer's Disease International.
Previous research also found an association between the shingles vaccine and a lower risk of dementia. But these studies were not able to adjust for the fact that people who get vaccinated may be overall more health-conscious than people who don't, possibly skewing the results linking the shingles vaccine and reduced dementia risk. A quirk in public health policy in Wales enabled Stanford researchers to control for these factors.
People who were 79 on Sept. 1, 2013, when the Welsh shingles vaccination program started, were eligible for the shingles vaccine for one year. People 80 and older would never be able to get vaccinated, because the policy was designed to ration a limited supply of the vaccine. This delineation meant that researchers could isolate the effect of being vaccinated by comparing people who turned 80 just before Sept. 1, 2013 to people who turned 80 right after that date.
"What makes the study so powerful is that it's essentially like a randomized trial with a control group — those a little bit too old to be eligible for the vaccine — and an intervention group — those just young enough to be eligible," Dr. Pascal Geldsetzer, an assistant professor of medicine at Stanford and the study's senior author, said in a statement.
The researchers also combed the health records for other factors, such as medications, that might have impacted the onset of dementia.
The shingles vaccine may lower dementia risk by decreasing neuroinflammation or by bolstering the immune system — or both, Geldsetzer told the New York Times.
Shingles is caused by the same virus that causes chickenpox, a virus that lingers in the body and can get reactivated, in the form of shingles, as people age. Shingles often appears as a line of blisters going around the torso. It is not life-threatening, but it can be very painful. The pain can last a long time after the blisters clear, according to the Mayo Clinic.