inclusion criteria: * health workers who are working onsite in patients' areas with covid-19 * age \> 18 years * negative specific igg and igm antibodies test result for sars cov-2 before the enrollment. * provide a signed and dated informed consent form

inclusion criteria: * health workers who are working onsite in patients' areas with covid-19 * age \> 18 years * negative specific igg and igm antibodies test result for sars cov-2 before the enrollment. * provide a signed and dated informed consent form

inclusion criteria: - health workers who are working onsite in patients' areas with covid-19 - age > 18 years - negative specific igg and igm antibodies test result for sars cov-2 before the enrollment. - provide a signed and dated informed consent form

inclusion criteria: - health workers who are working onsite in patients' areas with covid-19 - age > 18 years - negative specific igg and igm antibodies test result for sars cov-2 before the enrollment. - provide a signed and dated informed consent form