Fig 7. Pulmonary BCG immunization is effective at protecting against Mtb in EM exposed hosts.

Chronic oral exposure to EM results in systemic tolerance against mycobacteria. This tolerance generates poor immunity in a subsequent intradermal BCG vaccination scenario, and could lead to variable vaccine efficacy. However, because systemic tolerance is not present in the airways of hosts, pulmonary immunization generates robust immunity and is protective against Mtb challenge.