BCG was developed as a vaccine against tuberculosis (TB), but many studies have now confirmed its ability to induce potent protection against other infectious diseases in children. It has recently been shown that this may be linked to increased response of the innate immune system to several non-specific pathogens after BCG exposure, so called 'innate immune training'. This training ability of BCG has been shown for children and young adults. However, to our knowledge, no studies on the ability of BCG to induce innate immune training in adults >50 years of age have been conducted. Immune training in elderly is of interest since with increasing age, the immune system gets weaker, and responds less adequately to a number of infections, for instance influenza. Thus, if BCG is able to stimulate the innate immune system in mature adults as well, it could potentially reduce the risk of serious infections in elderly.