Several studies suggest a correlation between receiving common vaccines, including those against diptheria/tetanus and influenza, and a reduced risk of Alzheimer's disease, Allysia Finley reports for the Wall Street Journal.

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The link between vaccines and Alzheimer's risk

While multiple studies have shown a correlation between vaccination and a lower Alzheimer's risk, none have proven a causal link, Finley reports. Still, two decades' worth of research have produced some intriguing results.

According to Finley, one of the first studies to suggest a link was published in 2001. In that study, researchers tracked around 3,600 Canadians who were over the age of 65. After adjusting for age, sex, and education, they found that having been vaccinated for diphtheria/tetanus, poliomyelitis, or influenza correlated with a 59%, 40%, and 25% reduction in risk for Alzheimer's, respectively.

However, the study demonstrated only correlation, not causation, Finley writes. It also didn't account for other potentially influential variables, such as the fact that vaccinated people may have been more likely to get regular checkups and have fewer underlying medical conditions.

But more recent research seems to support the notion that vaccination is tied to a lesser Alzheimer's risk—even when those additional factors are controlled for, Finley writes.

For instance, a research article published in April in the Journals of Gerontology looked at the correlation between Alzheimer's and the tetanus, diphtheria, and pertussis (Tdap) vaccine using health records from the Veterans Health Administration and a database of private medical claims for adults over the age of 65. In that study, the researchers found—after adjusting for demographics, health services utilization, health conditions, and medications—those who received the Tdap vaccine had a 42% lower risk of developing dementia compared with those who hadn't.

Similarly, a study published this spring in Vaccines looked at the health records of 12,185 bladder cancer patients in Israel and the United States from 2000 to 2019. It found that patients over 75 who had received BCG—a tuberculosis vaccine that's also used as treatment for bladder cancer—as a cancer treatment had a 27% lower risk of developing Alzheimer's between 3.5 to seven years later.

"We attributed BCG's beneficial effect on neurodegenerative diseases to a possible activation of long-term nonspecific immune effects," the study authors wrote. For example, the BCG vaccine was shown to increase levels of anti-inflammatory cytokines, which could increase the number of T-cells that help regulate inflammation, Finley reports.

Another study published this spring looking at BCG, from the Montefiore Medical Center and Albert Einstein College of Medicine, found that patients with bladder cancer who received the vaccine had a 60% lower risk of developing Alzheimer's and other dementias than patients who didn't receive the vaccine.

And a study published last year by the National Heart, Lung, and Blood Institute looked at data of more than 5,000 people aged 65 and older participating in a cardiovascular health study. It found that participants between the ages of 65 and 75 who received a pneumonia vaccine were 25% to 30% less likely to develop Alzheimer's.

Moreover, a separate study from the University of Texas' McGovern Medical School found that seniors who more frequently received influenza vaccines and got their first vaccine before age 60 were significantly less likely to develop Alzheimer's, Finley writes.

Could Covid-19 vaccines have a similar effect?

Because Covid-19 vaccines are so new, it's not yet clear whether receiving those vaccines is also tied to a lower risk of Alzheimer's.

However, according to Finley, Covid-19 vaccines do trigger a strong immune response similar to that prompted by some of the other vaccines that have been studied. For instance, the mRNA Covid-19 vaccines have been found to generate cytokines like those spurred by the BCG treatment, Finley writes.

Any direct benefit in reducing Alzheimer's risk would, of course, be in addition to the vaccines' main purpose: preventing Covid-19—a disease that may itself pose brain risks. Researchers at the Cleveland Clinic this summer found that Covid-19 infections "significantly altered Alzheimer's markers implicated in brain inflammation," Finley reports. (Finley, Wall Street Journal, 8/5)