2.1. Study population and timeline

Based on specific governmental measures implemented in Belgium during the pandemic, we identified three periods of interest: the first wave (starting from the discovery of the first case on 2 March until 21 June 2020), the inter‐wave period (22 June until 30 August 2020) and the second wave (from 31 August, ongoing). This study was performed in the second wave, from weeks 47 to 52 of 2020 (16 November to 27 December 2020).

The population of employees among 572 NHs was estimated to be 49,816, including trainees, volunteers and freelancers, but excluding people on leave, working part‐time, dismissed due to illness or unavailable at the time of testing. A maximum of 32,900 tests per week was set, corresponding to the estimated maximum at‐risk population at the time.