Q: I am an MBBS student and I want to know if a BCG injection leaves a scar? If the vaccine has less potency due to improper temperature maintenance, will there still be a scar? So, can the appearance of the scar be taken as a 100% proof that the body has taken up the vaccine and that the vaccine given was potent?

A:The appearance of a scar after BCG vaccination is taken as evidence of a successful uptake of the vaccine. If the potency of the administered vaccine is sub-optimal due to any reason (for example, improper temperature storage, less number of bacilli, improper reconstitution) or if it is improperly administered, there will be no scar formation.