Every three seconds, someone in the world develops dementia. As the global population ages, the number of people living with dementia is expected to more than double—from 78 million in 2020 to 139 million by 2050.
This makes dementia one of the most urgent public health challenges of our time. A new study from Canada suggests that a common vaccine might offer unexpected protection: the shingles vaccine, also known as Zostavax.
Researchers from Ontario looked at nearly 230,000 older adults who were born between 1930 and 1960 and were registered with primary care providers. They used a natural experiment, meaning they didn’t assign treatments themselves but instead studied the impact of a real-world policy change.
In 2016, Ontario introduced a free shingles vaccine program for people who turned 71 on or after January 1, 2017. This created two groups: people who became eligible for the free vaccine, and people just slightly older who did not.
The researchers then followed these two groups over time. They found that those who were eligible for the free shingles vaccine were less likely to be diagnosed with dementia over the next 5.5 years. Specifically, there was a 2 percentage point reduction in dementia diagnoses among vaccinated individuals.
The effect was strongest among people born in 1945 and 1946—the groups directly impacted by the vaccination policy. This pattern was not seen in other provinces that didn’t offer the vaccine for free or in people born in other years.
What makes this study stand out is its method. Most previous studies on shingles vaccination and dementia were observational. That means they simply looked at people who chose to get vaccinated and compared them with people who didn’t.
But people who get vaccines often live healthier lives overall, which could affect the results. This new study avoids that problem by using birth dates as a way to randomly divide people into groups, which is a stronger way to show cause and effect.
There’s a scientific reason why the shingles vaccine might help prevent dementia. Some viruses, including the herpes viruses that cause shingles, can affect the brain. As we age, these viruses can reactivate and may trigger harmful processes in the brain.
In fact, some studies have shown that herpes viruses can cause the buildup of proteins in the brain—like β-amyloid and tau—that are linked to Alzheimer’s disease.
Zostavax is currently the only vaccine used in clinics that targets a herpes virus that affects the nervous system. Earlier research hinted that it might lower the risk of dementia, but the evidence wasn’t clear.
This Canadian study adds stronger support to that idea, using data from primary care visits rather than insurance records for a more complete picture of patient health.
One surprising finding from the study was that the vaccine’s protective effect was much stronger in women than in men. The risk reduction in women was statistically significant, while in men it was not. This suggests that future research should look more closely at how sex and gender affect how vaccines work in older adults.
In the end, the researchers say that their findings offer stronger evidence than past studies and point to the possibility that vaccination could play a role in dementia prevention.
If future research confirms these results, public health officials may consider expanding access to the shingles vaccine—not just to prevent shingles, but also as a step toward reducing dementia risk.
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The study is published in The Lancet Neurology.
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