A century-old vaccine, a new use
The BCG (Bacillus Calmette-Guérin) vaccine, developed in 1921 to prevent tuberculosis, may have an unexpected benefit: protecting the brain against Alzheimer's disease. Researchers have found that BCG triggers measurable changes in brain immunity, specifically altering the activity of microglia — the brain's resident immune cells. Activated microglia appear more effective at clearing amyloid-beta plaques, a hallmark of Alzheimer's.
Real-world evidence emerges
Multiple studies have observed that patients who received BCG — often for bladder cancer treatment — showed lower rates of Alzheimer's compared to matched controls. The correlation was strong enough to warrant controlled clinical trials. Researchers believe BCG may work through 'trained immunity,' a phenomenon where the innate immune system retains a memory of past infections, enabling a faster and more effective response to future threats — including the protein aggregates that damage the brain.
Clinical trials in planning
Several research groups are now planning randomized controlled trials to test BCG as a preventive therapy for Alzheimer's in older adults. If successful, BCG would offer a cheap, safe, and widely available option for dementia prevention. 'BCG has a well-known safety profile and costs pennies per dose,' said one researcher. 'The potential global impact, especially in low-resource settings, could be enormous.' The World Health Organization has expressed interest in the findings and is monitoring the trial planning process.