July 10th, 2026
Vaccinations can produce a lasting effect known as trained immunity, altering the behavior of the innate immune system and resulting in both a reduction in the chronic inflammation of aging and a more effective immune response to unrelated infectious agents. Arguably the largest body of research into trained immunity involves the BCG vaccine for tuberculosis, widely used outside the United States. A lesser body of work examines the trained immunity effects of a small number of other vaccines that are more commonly provided to adults rather than children. For most vaccines, there is no human data, and trained immunity itself is well documented, but not well understood in detail. Here, researchers report on a small trial to assess the effects of BCG vaccination on older people with and without Alzheimer's disease, to see whether the changes produced by trained immunity are sizable enough to justify further trials and widespread use.
Immune aging may contribute to Alzheimer's disease. Bacillus Calmette-Guérin (BCG), a vaccine known to induce trained immunity, has been linked to reduced Alzheimer's risk in prior studies. However, whether trained immunity can be observed in the human central nervous system remains unclear. We conducted two related one-year, open-label clinical trials in adults aged 55 years or older (n = 12 without Alzheimer's-related pathology; n = 11 with Alzheimer's-related pathology) recruited at a single center. Participants received two intradermal BCG vaccinations one month apart.
