The American Academy of Pediatrics issued new guidance on Monday in support of returning to in-person school this fall, but recommended that all children, including those who have already been vaccinated, wear masks.

The AAP recommended universal masking because many school-age children are not yet eligible for vaccines. Officials have said that vaccines for children under the age of 12 will not be ready until midwinter, months after many schools are set to open for in-person learning.

“There are many children and others who cannot be vaccinated,” said Sara Bode, a doctor and chairperson-elect of the AAP Council on School Health executive committee.

Universal masking has proved effective in protecting people, according to Bode. She added that masking everyone is “the most effective strategy to create consistent messages and expectations among students without the added burden of needing to monitor everyone’s vaccination status.”

The AAP’s mask recommendation is at odds with guidance from the Centers for Disease Control and Prevention issued earlier this month that noted vaccinated students do not have to wear masks in classrooms.

In addition to recommending everyone wear masks, the AAP called for schools to be prepared to provide mental health support and adequate COVID-19 testing supplies and protocols. The organization also recommended that schools’ strategies be flexible and adaptable as the transmission and positivity rates will vary.