Study design
Data on the implementation of IPC measures were collected from schools at the start of the study in December 2020/January 2021, and again in March and May/June 2021. At these three data collection periods, saliva samples were taken from (the same) pupils and staff to determine the prevalence of anti-SARS-CoV-2 antibodies. A descriptive analysis of the implementation of IPC measures in Belgian schools is presented for each of the three data collection periods, but the association between the strength of implementation of IPC measures and the SARS-CoV-2 seroprevalence among pupils and staff, was only assessed in the data collected in December 2020/January 2021.