For years, public health officials have been trying to dispel
the myth that people who get a flu shot are more
likely to get Alzheimer's disease.
They are not. And now there is evidence that vaccines that
protect against the flu and pneumonia may actually protect people from
Alzheimer's, too.
The evidence comes from two studies presented Monday at this year's Alzheimer's
Association International Conference, which is being held as a
virtual event.
"We've always known that vaccines are very important to our
overall health," says Maria Carrillo, chief science officer of the
Alzheimer's Association. "And maybe they even contribute to protecting our
memory, our cognition, our brain."
The first study came from a team at the University of Texas that
combed through millions of medical records in a national database. The goal was
to find factors that affected a person's risk of getting certain diseases,
including Alzheimer's.
"And one of the things that came back was flu shots,"
says Albert Amran, a medical student of the McGovern Medical School at the
University of Texas Health Science Center in Houston and an author of the
study.
That seemed odd. So Amran and a team of researchers took a closer
look at the medical records of about 9,000 people who were at least 60 years
old. Some had received a seasonal flu shot. Some hadn't.
"We [tried] to make sure that both groups had an equal
amount of, say, smoking status, obesity, diabetes, cardiovascular
disease," Amran says. Those are known risk factors for Alzheimer's. The
team also looked at factors like education and income, and indicators like the
number of prescriptions a person had received, to make sure that people who got
vaccines weren't just healthier overall. They weren't.
Next the researchers looked to see who was most likely to be
diagnosed with the disease.
People who got at least one flu shot had a 17% reduction in
risk, Amran says. And people who got regular vaccinations saw their risk drop
another 13%.
"More vaccinations meant less Alzheimer's," Amran
says.
Degree of brain benefit might vary
But he cautions that the amount of benefit from flu vaccination
could be different in a different group of people.
"There is a protective effect," he says.
"How much is something that needs
to be quantified with a more intensive study."
Even so, the result was surprising, says Dr. Paul Schulz, director of the neurocognitive
disorders center at McGovern.
"To have these guys come out and say, well it looks like
getting the vaccine is associated with less [Alzheimer's] was totally the
opposite of what any of us thought," Schulz says.
He was surprised because vaccines tend
to cause inflammation when they stimulate the immune system. And in Alzheimer's
disease, he says, inflammation is part of the problem.
"Here we've got a situation where we're giving them
inflammation on purpose, and we get people who are actually doing better,"
Schulz says.
A second study looked at the effect of both flu and pneumonia
vaccines on Alzheimer's risk.
A team from Duke University and the University of North Carolina
studied the medical records of more than 5,000 people who were at least 65
years old.
Those who received a pneumonia vaccine before age 75 were at
least 25% less likely to be diagnosed with Alzheimer's, says Svetlana Ukraintseva, an associate research professor
in the Biodemography of Aging Research Unit at Duke's Social Science Research
Institute.
"Pneumonia vaccination appears to be protective for older
adults," she says.
But in this study, giving a flu vaccine in addition to the pneumonia
vaccine did not cause any additional reduction in risk, Ukraintseva says.
What's behind the brain protection
Scientists don't know why vaccinations might reduce the risk of
Alzheimer's. But previous research has hinted at a connection. And
there are several potential explanations.
One is that vaccines for the flu and pneumonia may be protective
because the two diseases they are designed to prevent are known to affect the
brain.
"Every time you have one of these infections you may
experience a challenge to your memory and thinking," Carrillo says. And
studies suggest that those events can increase a person's risk of Alzheimer's.
Another possibility involves evidence linking Alzheimer's to a
general weakening in the immune system and to changes that allow more bacteria
and viruses into the brain.
"So if we have some general means of improving immunity, it
might help reduce Alzheimer's disease," Ukraintseva says.
A number of vaccines, including those for flu and pneumonia,
might be capable of improving immunity overall, she says. Scientists are
looking at several other potential candidates, including vaccines against herpes viruses and tuberculosis.
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