Dec. 3, 2020 -- Could vaccines play a role in preventing Alzheimer’s disease?
Svetlana Ukraintseva, PhD, an associate research professor in the Biodemography of Aging Research Unit at the Duke University Social Science Research Institute, researched a possible link between the pneumonia vaccine and Alzheimer’s in a study released this year.
She says her team is now looking at the effects of vaccines on Alzheimer's disease on a larger group -- 50,000 people. She also plans to investigate whether other vaccines, beyond the flu and pneumonia shots, might boost immunity and protect against Alzheimer's, and how infections like pneumonia and herpes affect Alzheimer's risk.
"So we can compare not only how several different vaccines affect Alzheimer's disease, but also several different infectious diseases," she says. She expects to have results in about a month, and will disclose then which vaccines are under study.
The Pneumonia Vaccine
Ukraintseva’s study looked at data from more than 5,000 people, ages 65 and over, who were part of the Cardiovascular Health Study, which was sponsored by the National Heart, Lung, and Blood Institute. The authors found that getting a pneumonia vaccine between ages 65 and 75 reduced the risk of Alzheimer's disease by up to 30%. In people who didn't carry a specific Alzheimer's genetic risk factor -- called rs2075650 G -- the reduction in Alzheimer's risk was even better -- up to 40%.
Ukraintseva says she chose that particular genetic risk factor because it helps to regulate the blood-brain barrier. That barrier prevents viruses and other harmful substances from getting into the brain. A weakened barrier might contribute to Alzheimer's disease.
The Flu Shot and Alzheimer's
In another study this year, people who got one or more flu vaccines were 17% less likely to get Alzheimer's disease. Those who got their flu shot more often had an additional 13% lower risk. Getting the first flu shot earlier in life -- at age 60 -- seemed to offer better protection than waiting until age 70 to get the vaccine.
"Overall, we found that flu shots, and more frequent flu shots, were associated with less cases of Alzheimer's disease," says Albert Amran, a fourth-year medical student at McGovern Medical School at UTHealth, who led the study.
These aren't the only studies to link vaccines with a reduced risk of Alzheimer's disease. An older study of 4,000 people ages 65 and older found that people who'd been exposed to the diphtheria, tetanus, polio, or flu vaccine had a lower risk for dementia. In another study, people with chronic kidney disease who got the flu vaccine were 30% to 40% less likely to get dementia, compared to those who weren't vaccinated.
How Might Vaccines Protect Against Alzheimer's Disease?
Researchers don't know exactly, but they have a few theories. "Perhaps preventing the viral infection itself may protect against neurological [brain] complications of the infection," Amran says.
Another possibility centers on the immune system in general. As we get older, our immune system weakens, and it can't respond as quickly or as strongly to viruses and other threats as it did when we were young. It's also not as good at keeping harmful substances out of our brain, or as efficient at fixing any damage that does happen to the brain.
Vaccines not only prevent a specific type of infection, but they might also give the immune system an overall boost. "You have this activated immune response for maybe several months or years, which allows you to also be protected against a bunch of other diseases," Ukraintseva says.
It's also possible that people who get vaccinated take better care of their health in other ways -- for example, they eat a healthy diet and exercise -- which helps protect them from Alzheimer's disease. The authors of both studies tried to control for other healthy practices but couldn't confirm whether they played a role in Alzheimer's prevention.
Getting your recommended flu and pneumonia vaccines protects you against these infections and the complications they can cause. These two studies suggest that these vaccines might also offer an extra benefit by protecting you against dementia.
Vaccines could have another advantage, too. Because they boost the immune system response as a whole, they might help people live longer, Ukraintseva says. "The million-dollar question is to select all of the vaccines with that rejuvenating effect on the immune system. In this case, we will have two wins: preventing Alzheimer's, and probably some sort of anti-aging intervention."
The CDC recommends that everyone over age 6 months get a flu shot every fall, and that adults over 65 get a pneumococcal vaccine to protect against these infections.