COVID-19 surveillance in the Flemish school system: development of systematic data collection within the public health school system and descriptive analysis of cases reported between October 2020 and June 2021., Merckx, Joanna, Crèvecoeur Jonas, Proesmans Kristiaan, Hammami Naïma, Denys Hilde, and Hens Niel , BMC Public Health, 2022 Oct 15, Volume 22, Issue 1, (2022)