Participants will be randomized to either BCG vaccination or placebo. To test the innate immune system blood will be withdraw 3 times: before the intervention, 2 weeks and 3 months after the intervention. There is a maximum of 10 ml blood each time, plus 3 ml the first time for the Quantiferon. This is a small volume, with a maximum of 33 ml and should not cause any problems for participants. Quantiferon results will be used as a baseline to test if participants are sensitized to mycobacterium Tuberculosis. In the blood, the innate immune training effects of BCG we will investigated by studying how the immune cells respond when they are stimulated with bacteria or other pathogens, which can cause serious infections. Provided that BCG shows induced innate immune training in adults >50 years of age, a large randomized control trial will follow to see if BCG vaccination reduces the number of acute infections in adults >50 years of age in Guinea-Bissau.