The investigators hypothesize that children are less likely to become infected in theschool environment, compared to the household or outside the school setting. Primaryschools do not play a major role in SARS-CoV-2 spreading. They hypothesize that incidencelevel in schools is mainly a consequence of community transmission. The incidence levelin household and that the secondary attack rate in schools remains at least 5 times lowerthat the transmission level in households.