TB Vaccine Question

[PaulParkhead]

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

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

[Szlater]

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

@British National Formulary

BCG (Bacillus Calmette-Guérin) is a live attenuated strain derived from Mycobacterium bovis which stimulates the development of hypersensitivity to M. tuberculosis. BCG vaccine should be given intradermally by operators skilled in the technique (see below).

The expected reaction to successful BCG vaccination is induration at the site of injection followed by a local lesion which starts as a papule 2 or more weeks after vaccination; the lesion may ulcerate then subside over several weeks or months, leaving a small, flat scar. A dry dressing may be used if the ulcer discharges, but air should not be excluded.

@Another BNF article

Intradermal injection technique:

Skin is stretched between thumb and forefinger and needle (size 25G or 26G) inserted (bevel upwards) for about 3 mm into superficial layers of dermis (almost parallel with surface). Needle should be short with short bevel (can usually be seen through epidermis during insertion). Tense raised blanched bleb showing tips of hair follicles is sign of correct injection; 7 mm bleb ≡ 0.1 mL injection, 3 mm bleb ≡ 0.05 mL injection; if considerable resistance not felt, needle too deep and should be removed and reinserted before giving more vaccine.

To be injected at insertion of deltoid muscle onto humerus (keloid formation more likely with sites higher on arm); tip of shoulder should be avoided.

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.