The Heaf test (pre-BCG) was to see if you reacted - that is, had already been exposed to TB.That was and is inevitable. There are people allergic to everything. It doesn't mean that the British were wrong in releasing the vaccine. It is probable that the Oxford one will affect different people, so in time a mix and match strategy will be adopted. Going back 60 years, I remember the tests for the BCG and that people were looking to see if they would take or react..I don't recall whether getting blisters was a good or bad outcome.
Blisters were unpleasant and excluded you from receiving the BCG. They would (at least sometimes) send you for a X-ray to see if there was any evidence in the lungs of previous infection. If so, repeat X-rays every year, at least for a while.