BCG-Induced Immune Training: Interplay between Trained Immunity and Emergency Granulopoiesis

•Mechanisms of BCG vaccine-mediated pathogen agnostic effects in part related to TI and EG.•Current evidence suggests EG may be the initial phase of TI.•The precise molecular mechanisms by which BCG begins to induce EG/TI is lacking.•BCG is unknown if EG/TI differs across variations in age and route of administration.•How BCG impacts on EG/TI across different age groups or through different routes of delivery is still unknown.