inclusion criteria: - age ≥ 18 years - negative pcr and negative serology on day 0 - healthcare worker at any of the trial sites - female participants: negative for pregnancy test - willing to participate in the study - able to sign the informed consent form

inclusion criteria: - age ≥ 18 years - negative pcr and negative serology on day 0 - healthcare worker at any of the trial sites - female participants: negative for pregnancy test - willing to participate in the study - able to sign the informed consent form