Can Vaccinations Save Your Brain?

​How do vaccines work against dementia?

One theory is that infectious agents -- such as the herpes virus that causes chickenpox and stays dormant in the body and can cause shingles years later -- play a role in developing Alzheimer's disease. ​​"There is some evidence that herpes viruses are a risk factor for dementia and so preventing active infection might slow down this process," Harrison says. Another explanation worth considering, he adds: "The new shingles vaccine contains adjuvants -- chemicals that increase the immune system's response to the vaccine--and maybe they have an unexpected beneficial effect on brain health."​

Schulz speculates that vaccination may reduce the immune system in the brain that is involved in attacking amyloid plaque (a protein found in abnormally high levels that clumps together in the brains of Alzheimer’s patients) as an invader. Attacking these plaques sounds like a good idea, but the immune reaction may cause chronic brain inflammation and the death of nearby cells.

“The problem in Alzheimer’s is that the immune system keeps trying to get rid of the plaque, and it can’t,” Schulz explains. “The plaque sits there for 10 years, and the immune system keeps throwing poisons at it all that time and is killing brain cells in the process.”

Or maybe the opposite happens: The vaccines enhance the ability of the immune system to remove amyloid plaques, he says. 

In the new shingles study, published in Nature Medicine in July, researchers at the University of Oxford studied more than 200,000 people 65 and older, comparing those who got the new shingles vaccine, Shingrix, with those who got the old, Zostavax, and found at least a 17 percent reduction in dementia diagnoses in the six years following vaccination with Shingrix. That equates to 164 or more additional days lived without dementia, according to the scientists.

“Other studies had shown that Zostavax - and most other vaccines - ‘beat’ no vaccination, so the Shingrix effect would look even bigger,” if you compared Shringrix to no vaccine, Harrison says.

These latest data build upon previous research by Schultz and others suggesting vaccines convey similar protective effects against cognitive decline.

Benefits of other vaccines

Schulz was the senior author of an earlier study that found a statistically significant difference in the incidence of Alzheimer’s between those vaccinated against the flu and unvaccinated people.

Two groups of 935,887 each were obtained from a national U.S. patient database. To ensure a valid comparison, both groups shared many of the same characteristics and risk factors, including age, gender and conditions such as hypertension, Schulz says — except one group was vaccinated and the other was not.

Patients who received at least one flu vaccine during the follow-up period of four years were 40 percent less likely to develop Alzheimer’s compared with those who did not get the vaccine. In addition, those who received an annual flu shot had the lowest rate of the disease.

“The more vaccinations you got, the better,” Schulz says.

His team has also been studying the effects of vaccines for other infectious diseases, including shingles, pneumococcal pneumonia and the combination of tetanus, diphtheria and pertussis (whooping cough), known as Tdap, with similar findings, he says. 

Pascal Geldsetzer, M.D., assistant professor of medicine at Stanford University, has run studies in large groups of older adult in Wales and Australia, also finding a benefit of shingles vaccination against dementia.

“This evidence suggests that the vaccine really could have benefits for delaying or preventing a condition that most people find even scarier than shingles,” Geldsetzer says.

The accumulating evidence suggests that getting your vaccines pays compelling and unexpected dividends, starting with an annual flu shot every fall. Virologist Robert T. Schooley, M.D., an infectious disease specialist at the University of California, San Diego — who has not been involved in any of the studies — says of the flu vaccine research, it is “certainly plausible” that reducing the frequency and severity of influenza through vaccination can quell immune activation over time.

Though Schooley and others suggest some caution when interpreting the results.

"It is also possible that the differences in [cognitive] decline were associated with other factors for which vaccination might be a marker rather than a cause,” he says. “Access to vaccination could be an indicator of more access to health care, better socioeconomic status, more mobility or other factors that would favor better neurologic outcomes."

Schooley’s  final note:

“One thing is for certain: Whether or not this observation is real, staying up to date with vaccinations for influenza and other infectious diseases as we age is a good idea.”