inclusion criteria: * 18 years of age or older to participate. * healthcare workers with primary practice in intensive care unit, general internal medicine, * covid-19 testing centres, emergency rooms, and nursing homes. * covid_19 symptom free at the time of randomization and have a negative diagnostic swab.

inclusion criteria: * 18 years of age or older to participate. * healthcare workers with primary practice in intensive care unit, general internal medicine, * covid-19 testing centres, emergency rooms, and nursing homes. * covid_19 symptom free at the time of randomization and have a negative diagnostic swab.

inclusion criteria: - 18 years of age or older to participate. - healthcare workers with primary practice in intensive care unit, general internal medicine, - covid-19 testing centres, emergency rooms, and nursing homes. - covid_19 symptom free at the time of randomization and have a negative diagnostic swab.

inclusion criteria: - 18 years of age or older to participate. - healthcare workers with primary practice in intensive care unit, general internal medicine, - covid-19 testing centres, emergency rooms, and nursing homes. - covid_19 symptom free at the time of randomization and have a negative diagnostic swab.