2000 health care workers in NHS Tayside and from social care will have blood samples tested to detect antibodies to SARS-CoV-2, to identify undiagnosed asymptomatic healthcare worker infections with COVID-19. Up to 20% of cases of COVID-19 disease in some countries have been reported to be healthcare workers. The prevalence of HCW infections has not been properly documented due to lack of comprehensive studies. This information is crucial for infection control and to maintain the workforce during a pandemic. In addition, as HCWs are frequently exposed to infected patients they represent an ideal population in which to characterise immune responses to the infection. Discovering the frequency and impact of HCW infections will allow better workforce planning in the NHS as well as establishing whether a positive antibody test can allow staff to safely return to work with a low risk of infection. 2000 HCW in NHS Tayside and from social care will have blood samples tested with a validated laboratory assay to detect antibodies to SARS-CoV-2. The aims of the study are to identify undiagnosed asymptomatic healthcare worker infections with COVID-19, to understand the burden of undetected infections and to identify in patients with detectable antibodies can be reinfected with COVID-19.