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The 100-year-old tuberculosis vaccine Bacillus Calmette-Guerin (BCG) vaccine may likely reduce risk of Alzheimer's disease and related dementias, suggests a study.

The BCG vaccine offers multiple beneficial effects, and it's currently a recommended therapy for non-muscle-invasive bladder cancer.

The findings, published in JAMA Network Open, revealed that treatment with the BCG vaccine was associated with a 20 per cent lower risk of Alzheimer's disease and related dementias.

The protective association was greater in patients aged 70 years or older, and also reduced risk of death.

Researchers from the Massachusetts General Hospital (MGH) and Brigham and Women's Hospital (BWH), followed 6,467 individuals for up to 15 years after they were diagnosed with non-muscle-invasive bladder cancer.

The group included 3,388 patients who underwent BCG vaccine treatment and 3,079 who served as controls, matched by factors such as age, sex, and medical comorbidities.

During follow-up, 202 patients in the BCG vaccine group and 262 in the control group developed Alzheimer's disease and related dementias.

The incidence was 8.8 per 1,000 person-years and 12.1 per 1,000 person-years in the respective groups.

In addition, 751 patients in the BCG vaccine group died while 973 people died in the control group. Thus, treatment with BCG vaccine was also associated with a 25 per cent lower risk of death.

"A vaccine like BCG, if proven effective, is a perfect example of a cost-effective, population-healtha"based solution to a devastating illness like Alzheimer's disease," Marc Weinberg, an Instructor in Psychiatry at MGH.

"We are shifting our focus towards studying the potential benefits of BCG vaccination of older adults in Alzheimer's disease-related clinical trials," he added.

If a causal link is found, it will be important to understand the mechanisms involved. Weinberg and his colleagues note that the BCG vaccine's effects on the immune system may play a role.