TB Vaccine Question

I guess this has a factual answer, so here we are:

As a baby, and again around age 13, I was vaccinated against tubercullosis. As a result, I now have two scars on my upper arm where the vaccination gadget put the stuff in (don’t you just love that medical terminology?)

But why? Why did this vaccination create scars? Other ones I’ve had, well, you’d never know it.

The vaccine was referred to as “BCG” and was, in the latter case at least, delivered by means of a silvery thing that went “Phut!”. More technical terms, I know :wink:

Edit to add: Place, Scotland; Year, 1972 and 1985

I had BCG at about 13, but it was given as an injection by a normal hypodermic needle. It caused a scar too.

So the injection is given into the skin, where the vaccine stimulates an immune response. This immune response causes a papule to form (sometimes it ulcerates), which ends up as a scar.