Hope for the Brain

Doctors and researchers are garnering ever more evidence that viruses can damage the brain and increase the risk of dementia. They also continue to validate the protective effects on the brain from all vaccines. At the same time, vaccine hesitancy is increasing due to political opposition; while hesitancy about new tests that detect early signs of Alzheimer’s disease comes mostly from the absence of effective treatment.

Absent, too, are ways to prevent the infections most clearly linked to dementia—several herpes viruses and pneumonias, Lyme disease, and gum disease—for which there are no vaccines, according to the Alzheimer’s Society. A multi-center consortium of Chinese researchers looking at 17 studies—with 1,857,134 participants altogether—concluded that “bacterial, fungal, and viral infections may cause neurotoxic inflammation and oxidative stress in the brain, which can lead to neurodegeneration.”

A recent “natural” or accidental experiment involving the shingles vaccine led to the clearest documentation of damage to the brain caused, in this case, by herpes viruses, which affect about 95% of the population and can remain dormant in the brain forever. Of eight herpes viruses that affect humans, Herpes Simplex virus (HSV) causes HSV-1 and HSV-2; while Varicella-Zoster virus (VZV) causes chickenpox as well as shingles, and is the most common re-activator of dormant herpes.

When the Welsh government initially offered the vaccine only to applicants aged 79 to 80, there was a chance to compare people one week younger than 80 who received the vaccine with those just one week older. At the end of seven years, those who had received the shingles vaccine were 20% less likely to develop dementia than the unvaccinated. Said Stanford University medical professor Pascal Geldsetzer, “It was really a striking finding.”

“This huge protective signal was there, any which way you looked at the data,” Geldsetzer added. Earlier research had been unable to separate out lifestyle variables among those who chose not to have various vaccines from the generally healthier group who chose to get them. But Geldsetzer noted, “If you take a thousand people at random born in one week and a thousand people at random born a week later, there shouldn’t be anything different about them on average.”

Comparing vaccinated versus unvaccinated populations, the Chinese researchers found a 35% lower risk of dementia associated with all vaccinations—including flu, pneumonia, shingles, Tdap (tetanus, diphtheria, and pertussis), and those protecting against rabies and hepatitis B. All vaccines may help protect against dementia, because any infection can reactivate dormant herpes virus in the brain.

Looking at records from 120 million patients across the U.S., a study at the University of Texas confirmed that people with a history of HSV infections had up to 2.44 times higher odds of developing dementia compared to those who never had it. Also, in 752,205 patients over age 45 followed between 2006 and 2017, VZV and HSV infections each increased the risk of dementia, according to researchers in Seoul, South Korea, while people with both infections—varicella and herpes — had the shortest time from infection to their dementia diagnosis.

Looking at flu vaccines, people who received at least one “were 40% less likely than their non-vaccinated peers to develop Alzheimer’s disease over the course of four years,” reported neurologists Avram Bukhbinder, now at Mass General, and Paul Schultz at University of Texas, Houston. Their research looking at the effects of flu vaccination on a large nationwide sample of adults age 65+ also showed that “the strength of this protective effect increased with the number of years that a person received an annual flu vaccine.”

“I think there’s a big push now for immunomodulation for Alzheimer’s and other degenerative diseases,” UCSF psychiatrist Kristine Yaffe said about the vaccine research. Besides protecting against specific infections, off-target or non-specific effects of vaccines could include training the body’s immune system to prevent pathogens from entering the brain, where they can cause chronic and abnormal neuroinflammation.

Among other measures for protecting the brain, the largest lifestyle intervention trial in the U.S., known as U.S. POINTER, has found that simultaneously targeting multiple areas—nutrition, exercise, cognitive training, health monitoring—improved cognitive measures of those at risk of dementia. In addition, participants in the structured group improved more than those who were self-guided. And carriers of the APOE4 gene, who have a higher risk of developing Alzheimer’s, benefited most significantly from sticking to a Mediterranean diet.

Healthy sleep habits are another protective measure against risky infections. And the current popularity of dental implants may come from evidence linking dementia to oral infections, which can trigger chronic inflammation throughout the body and weaken the blood-brain barrier, making it easier for infections to enter the brain. In addition, missing teeth can reduce stimulation to the brain from chewing. Finally, protection against Lyme-infected ticks with specially treated clothing is becoming more available.

But “the only thing most scientists would agree on which does affect the ability of your immune system to respond to an infection is stress,” according to British immunologist Daniel Davis, author of the 2025 book Self Help: A Myth-Busting Guide to Immune Health. “There’s a molecular level of understanding of why that is: because when you are stressed the cortisol levels in your blood go up and that quietens down the immune system because you divert energy to the fight-or-flight response.”

2025 also brought the new test for Alzheimer’s disease, with 90% accuracy, according to The New York Times, that measures two key protein biomarkers: amyloid beta and P-tau 217. “P-tau 217 seems to be the most informative with regard to the likelihood of the person having underlying Alzheimer’s disease biology,” Mayo Clinic neurologist Ronald Petersen told The Washington Post. Initial research found the test most accurate in people who already had symptoms of dementia or mild cognitive impairment, and the test also comes with a risk of false positive results—as more than 20% of adults who were not cognitively impaired tested positive for amyloid proteins.

The lack of effective treatment for Alzheimer’s, the main reason for hesitancy about taking the test, may also be adding to our already immunity-reducing levels of stress. Over time I have contracted many of the risky infections and have obtained every vaccine possible, including Covid vaccines in the spring and fall. Lately, though, I have also been trying to follow the sign-off advice now appearing on some friends’ emails: “Just Breathe deeply.”