BCG is a vaccine that helps the body fight tuberculosis (TB), a serious disease that often attacks the lungs. It is made from a weak cousin of the TB germ, so the body can practise without getting the full illness. In Taiwan, babies usually get a BCG shot, and many people still have a small round scar on the upper arm from it. It has been used around the world for many decades. Though actually, it is not a perfect shield: it helps a lot against some dangerous forms of TB in children, and rather less against every kind of TB in adults. You will hear BCG in clinics and health class, not in ordinary chat, unless someone is talking about that scar. It is not a shot for a cold, for flu, or for COVID.