inclusion criteria: - adult > 18 years old - both gender (male and female) - healthy health care workers employed by one of the hospitals involved in the study - negative serology at day 0 for covid19 infection. - evidence of a personally signed and dated informed consent document

inclusion criteria: - adult > 18 years old - both gender (male and female) - healthy health care workers employed by one of the hospitals involved in the study - negative serology at day 0 for covid19 infection. - evidence of a personally signed and dated informed consent document