Fig 1. Flowchart of the inclusion process.

Flowchart of the inclusion process of healthcare workers. *Defined based on PCR tests only. Severe COVID-19 was defined as any hospital admission longer than 48 hours with time of admission within 14 days after the positive SARS-CoV-2 test result. **Defined based on PCR tests and ELISA tests. Abbreviations: PCR, polymerase chain reaction. SARS-CoV-2, Severe Acute Respiratory Syndrome Coronavirus-2.