Introduction. In early January 2020, the pandemic of COVID-19 (coronavirus disease 2019) rapidly spread from China and caused a worldwide pandemic.Hypothesis. Healthcare workers represent a high-risk group for acquiring COVID-19 and for nosocomial transmission of severe acute respiratory coronavirus 2 (SARS-CoV-2).Aim. We aimed to investigate over a 1 year period, across two pandemic waves, the SARS-CoV-2 seroprevalence in employees at a Western Switzerland public hospital.Methodology. A prospective observational SARS-CoV-2 seroprevalence study was proposed to all hospital employees who enrolled on a voluntary basis.Results. Out of 594 participants recruited on a voluntary basis, 269 volunteers (45.3 %) had anti-SARS-CoV-2 antibodies: this seroprevalence was twice higher than that reported in the local community. Healthcare workers with prolonged exposure to patients with COVID-19 showed a significantly higher odds ratio (OR) of having a positive SARS-CoV-2 serology [OR 3.19, 95 % confidence interval (CI) 2.16-4.74]. Symptoms showing the highest association with a positive serology were anosmia (OR 11.9, 95 % CI 5.58-30.9) and ageusia (OR 10.3, 95 % CI 4.8-26.3). A total of 17.1 % (95 % CI 12.2-21.1 %) of SARS-CoV-2 seropositive volunteers did not report a suspicion of COVID-19 in their personal history.Conclusion. Overall, we observed that the impact of the second SARS-CoV-2 pandemic wave was considerable and significantly affected healthcare workers with prolonged exposure to patients with COVID-19.