Does WHO recommend staff and children to wear masks at school? And if yes, what type of masks?

The decision to wear a mask depends on the assessment of risk. For example, how extensive is COVID-19 in the community? Can the school ensure physical distance of at least 1 metre from others? Are there students or teachers with underlying health conditions?

Fabric masks are recommended to prevent onward transmission in the general population in public areas, particularly where distancing is not possible, and in areas of community transmission. This could include the school grounds in some situations. Masks may help to protect others, because wearers may be infected before symptoms of illness appear. The policy on wearing a mask or face covering should be in line with national or local guidelines. Where used, masks should be worn, cared for and disposed of properly. 

It is important that anyone feeling unwell should stay at home and call their health provider.