Federal health officials stepped up calls for parents and officials to implement safety measures such as universal masking in schools as students return to in-person classes, citing outbreaks that forced many children back to temporary remote learning.

“In our outbreak investigations, large scale quarantines or a large number of cases are generally occurring in schools because schools are not following our guidance, particularly our recommendations for teachers as well as students aged 12 and over to be vaccinated and for everyone right now to be masked,” Centers for Disease Control and Prevention Director Rochelle Walensky said Friday.