The real-world effectiveness of preschoolers wearing masks on campus to prevent respiratory infectious diseases: a cohort study

Indoor mask-wearing did not reduce the incidence of respiratory infections in preschoolers in a real-world campus setting. However, this study included a small number of preschoolers and observed them for a short period of time. Preschoolers were instructed to wear masks only when indoors. These factors could lead to bias and limit the generalizability of the study results.