A century-old vaccine may have an unexpected role in protecting the brain
Study suggests the BCG tuberculosis vaccine may alter levels of amyloid beta protein, offering new clues about why it has been linked to a lower risk of Alzheimer's disease.
- 9 July 2026
- 4 min read
- by Linda Geddes
At a glance
- Previous studies had indicated that the Bacillus Calmette–Guérin (BCG) tuberculosis vaccine might be associated with a reduced risk of Alzheimer’s disease as well as boosting defences against unrelated infections.
- To investigate, researchers followed older adults for a year after BCG vaccination, analysing blood and cerebrospinal fluid to see how vaccination affected the immune environment in and around the brain.
- They found that BCG vaccination changed how immune cells behaved and altered levels of amyloid beta, a protein that accumulates in the brains of people with Alzheimer’s.
A new study has uncovered a potential mechanism that links the BCG tuberculosis vaccine with a lower risk of Alzheimer’s disease.
The researchers found that the Bacillus Calmette–Guérin (BCG) tuberculosis vaccine appears to increase the responsiveness of immune cells surrounding the brain and alter levels of a key protein associated with Alzheimer’s disease.
Previous studies have hinted that the vaccine might be associated with a reduced risk of Alzheimer’s disease, as well as boosting defences against unrelated infections. However, the mechanism underpinning these potentially beneficial effects had been unclear.
The new study followed older adults for a year after BCG vaccination, analysing blood and cerebrospinal fluid to investigate how the vaccine affects the immune environment in and around the brain.
Although it was a small study and further research is needed, the findings may help to explain previous observations linking BCG vaccination to a lower risk of Alzheimer’s disease.
“The immune system and the brain may be far more connected than we once thought,” said the study’s senior researcher, Dr Steven Arnold of the Interdisciplinary Brain Center at Mass General Brigham Neuroscience Institute in Boston, US.
What is the BCG vaccine?
The BCG vaccine is one of the most widely used of all current vaccines and provides significant protection against tuberculosis (TB) disease in infants and young children. It contains different attenuated strains of Mycobacterium bovis bacteria and is given by injection just under the skin (intradermally).
Since it was first introduced around a century ago, various studies have indicated that BCG vaccination may also strengthen defences against unrelated infections by triggering long-term changes in innate immune cells that provide a first line of defence against invading microbes.
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More recently, researchers have discovered that the vaccine can induce so-called “trained immunity”, a form of immune memory in which these innate immune cells are reprogrammed to respond more effectively to future threats, while also influencing broader immune activity.
Since many age-related diseases, including Alzheimer's disease, are associated with chronic, low-grade inflammation, scientists have begun investigating whether these effects could also help to moderate harmful inflammatory responses.
How does the BCG vaccine affect immune responses in and around the brain?
The latest study set out to investigate whether this trained immunity also extended to immune cells in the central nervous system, including those in the fluid surrounding the brain and spinal cord.
Arnold and his colleagues recruited 23 adults aged 55 years and older, including 11 with biological changes associated with Alzheimer’s disease and 12 without.
All of them received two intradermal doses of the BCG vaccine one month apart, before providing blood and cerebrospinal fluid samples at regular intervals over the following year.
The researchers analysed these samples for changes in immune activity, as well as levels of proteins linked to Alzheimer’s disease. This included amyloid beta, a protein known to accumulate in the brains of people with Alzheimer’s.
The research, published in Communications Medicine,found that BCG vaccination changed how immune cells behaved: they responded more vigorously to molecules designed to mimic infection, without increasing background levels of inflammation – a known risk factor for neurodegeneration.
Vaccination also altered levels of amyloid beta in the blood and cerebrospinal fluid of people without Alzheimer’s-related biological changes, but not those who already had such changes.
This could suggest that the timing of vaccine administration could be important, although the study was too small to draw firm conclusions. It also didn’t examine the impact of BCG vaccination during childhood.
“Vaccines have traditionally been viewed through the lens of infectious disease prevention. Although more research is needed, these findings suggest they may also influence biological processes involved in brain aging and neurodegenerative disease,” said Dr Marc Weinberg, research scientist at Mass General Brigham in Boston, US, who led the study.
“The next step is to test this rigorously in larger, controlled studies, particularly in prevention, where the hope would be to preserve brain health before significant Alzheimer’s disease develops,” said Arnold.
