inclusion criteria: * a health care professional (physician, nurse, midwife, paramedic, electroradiology technician, laboratory diagnostician, physiotherapist, nutritionist, orderly) aged \>25 years * no confirmed sars-cov-2 infection * informed consent to participate in the trial and consent to personal data processing * declared availability for telephone contacts throughout the study period * good health condition * earlier vaccination against tuberculosis

inclusion criteria: * a health care professional (physician, nurse, midwife, paramedic, electroradiology technician, laboratory diagnostician, physiotherapist, nutritionist, orderly) aged \>25 years * no confirmed sars-cov-2 infection * informed consent to participate in the trial and consent to personal data processing * declared availability for telephone contacts throughout the study period * good health condition * earlier vaccination against tuberculosis

inclusion criteria: - a health care professional (physician, nurse, midwife, paramedic, electroradiology technician, laboratory diagnostician, physiotherapist, nutritionist, orderly) aged >25 years - no confirmed sars-cov-2 infection - informed consent to participate in the trial and consent to personal data processing - declared availability for telephone contacts throughout the study period - good health condition - earlier vaccination against tuberculosis

inclusion criteria: - a health care professional (physician, nurse, midwife, paramedic, electroradiology technician, laboratory diagnostician, physiotherapist, nutritionist, orderly) aged >25 years - no confirmed sars-cov-2 infection - informed consent to participate in the trial and consent to personal data processing - declared availability for telephone contacts throughout the study period - good health condition - earlier vaccination against tuberculosis