Phase 4 Study design: A placebo-controlled adaptive multi-center randomized controlled trial.

Study population: 1800 High-risk HCW with direct patient contacts, defined as physician assistants, respiratory therapists, nurses, physicians or other HCWs working at emergency rooms, ICUs and in locations within hospitals where COVID-infected patients are treated.

Intervention: Participants will be randomized between intradermal administration of BCG vaccine or placebo in a 1:1 ratio.