Massive BCG blister on 5 month old

[MakeTeaNotWar]

DS is 5 months old. He had his BCG jab in December and the blister has become progressively larger. It is now the size of a large marble and basically takes over his tiny arm. The health visitor couldn't tell me if this was normal and google is confusing. Anyone any experience? Doesn't seem to bother him but really is very large

Yeah mine had that - huge & gross but didn't seem to bother him. It took months and months to go down. It's still quite a large red mark, albeit flat now (over a year later).
I seem to remember the same thing when I had mine, aged 11ish.

It's just popped! Lots of green pus beurk

yep, normal, and it will dry again and then weep again whenever you get it wet in the bath and dry again and so on... I think it took quite a few months until it was settled