A relatively mundane middle-aged rite of passage — shingles vaccination — might offer an added benefit: protection against, or even the slowing of the progression of, dementia.

Over the past several years, a growing body of research has suggested that immunization against shingles may reduce the risk of dementia by up to 20%. Now, a new study adds a tantalizing twist: the vaccine may also have a therapeutic effect in those who already have the condition. This wasn’t a modest effect, either — the shot appeared to lower the risk of death associated with dementia over the course of almost a decade by nearly 30%.

The findings are yet another reminder of the remarkable and often unexpected ways that vaccines can protect us well beyond their intended role of preventing infection. And if the findings hold up in more rigorous studies, the results could point to a relatively inexpensive and widely available tool with the potential to meaningfully improve population health. That would be an astounding development.

Anyone who has had chickenpox is at risk of shingles, characterized by a painful, blistering rash. That’s because the varicella-zoster virus that causes chickenpox hibernates in our nervous system until it re-emerges later in life.

What, then, could a vaccine against shingles possibly have to do with dementia?

Researchers have two plausible theories. The first focuses on the virus itself. If the chickenpox virus is repeatedly activated and then suppressed by the immune system, it could cause brain inflammation that contributes to dementia, says Pascal Geldsetzer, a Stanford University population health scientist who led the vaccine study.

That theory aligns with what we know about the sneaky ways viruses can wreak havoc long after we’ve recovered from an infection.

Increasing evidence has also linked the Epstein-Barr virus — a member of the same herpesvirus family — to multiple sclerosis. The theory is that the virus features a protein that resembles one found in the brain and spinal cord, so when the immune system mounts an attack, it mistakenly chips away at the protective coating on nerve cells. (Several groups are working to develop a vaccine against Epstein-Barr in the hope that it might protect against multiple sclerosis, too.)

The other hypothesis rests on some vaccines’ ability to offer broader health benefits — benefits that come not from targeting the virus, but from triggering the immune system to be on the hunt for bad actors.

For example, researchers recently found that mRNA-based COVID vaccines might extend the lives of certain cancer patients. This effect appears to result from enhancing the immune system at precisely the right time, enabling it to eliminate tumors more effectively. A large body of work indicates that a tuberculosis vaccine offers protection against other infections and, notably, has reduced the infant mortality rate in some countries. More recent research suggests that this Bacillus Calmette–Guérin (BCG) vaccine may also reduce the risk of dementia.

Researchers, meanwhile, also need to address two big caveats about these findings. The first is that the connection is based on studies that looked back at people who did or did not receive the shingles vaccine, rather than on randomized, placebo-controlled trials that can definitively establish an effect. To be fair, these were unusually robust observational studies that compared people born within weeks of each other in the UK, either before or after a strict age cutoff for vaccination.

The second has perhaps greater real-world implications: the studies all rely on data collected when people were receiving the older shingles vaccine, Zostavax, which is no longer used in the U.S. or Europe. That shot was made from a weakened form of the varicella-zoster virus, whereas the current vaccine, Shingrix, exposes the immune system to only a portion of the virus.

Does the effect hold up with the current shot, which the Centers for Disease Control and Prevention made the preferred choice in 2018? We just don’t know. If the benefits come from shutting down the virus, they may be as good or even better with the newer vaccine, which is far more effective and longer-lasting than the old one. But if the way the vaccine triggers the immune system’s response is what matters, then the newer shot might not help.

It is also worth exploring whether a booster could extend those benefits. And what does all of this mean for younger generations who have grown up with the chickenpox vaccine? While many Gen Xers and older Millennials have visceral memories (and maybe a few scars) from their days of itchy misery from chickenpox, a vaccine against varicella was added to the routine childhood immunization schedule in 1996. It will be decades before we determine whether lifelong protection from chickenpox affects brain health.

All of these questions need to be explored in the lab and in clinical trials. Geldsetzer has been trying to raise money to conduct a randomized controlled trial of the older vaccine to conclusively determine its effectiveness in preventing or treating dementia. Getting that off the ground has been a slog. He told me about his plans to run the trial two years ago, and yet the funding still hasn’t materialized.

Let’s hope that changes as evidence of these potentially significant additional benefits of vaccination mounts. Ideally, such a trial would also examine the current shingles vaccine, too. After all, if the effect holds up, it could mean the world would have a relatively inexpensive, one-time intervention to lower the risk of dementia, or even slow it down. That’s something everyone surely would be clamoring to get.

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This column reflects the personal views of the author and does not necessarily reflect the opinion of the editorial board or Bloomberg LP and its owners.

Lisa Jarvis is a Bloomberg Opinion columnist covering biotech, health care and the pharmaceutical industry. Previously, she was executive editor of Chemical & Engineering News.

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