Kids are heading back to school in person after a year of remote or online learning. Amid mounting COVID-19 transmission before children return to classrooms, the CDC guidelines recommends mask-wearing in schools among students, staff and teachers to protect children who aren't eligible for vaccines. The more aggressive transmission of the delta variant is worrisome and prompted the tougher masking guidelines, said Rochelle Walensky, director of the CDC. The guidance is a major change from the CDC's recommendations this month that vaccinated students and staff need not mask up in schools. The CDC recommended everyone in communities with substantial virus transmission wear masks indoors. Many schools, particularly in Southern and Republican-led states, have dropped those requirements while planning to return thousands of unvaccinated children to classrooms. “The CDC is doing the responsible thing by altering their recommendations as we’ve seen rising infection rates across the country,” said Lewis Nelson, chair of emergency medicine at Rutgers University Medical School in New Jersey. Although young children rarely get very sick from COVID-19, infections have climbed this summer as the delta variant spread. About 4.1 million children have had a diagnosed case, resulting in about 18,000 hospitalizations and more than 350 deaths.