Fig. 1.

Vaccines excite the initiation of the adaptive immune response and the development of immunological memory.^25,26 The immunological memory consists of the developments of antigen-specific T and B cells which protects against subsequent insult by the pathogen. This is thought to be due to secondary innate immune response induced by BCG vaccination, coined as nonspecific effects (NSEs). The efficacy to protect against other infections can be linked to its immunological memory eliciting lymphocytes response (Fig. 1) and trained immunity (Fig. 2, Fig. 3).