SACRAMENTO (CBS SF) – California public health officials announced Monday that K-12 students will be required to wear masks indoors at schools once the upcoming school year begins.

“Masks are one of the most effective and simplest safety mitigation layers to prevent in-school transmission of COVID-19 infections and to support full time in-person instruction in K-12 schools,” the California Department of Public Health said in a statement.

The announcement comes after the Centers for Disease Control announced it was relaxing its guidelines regarding schools, saying that vaccinated teachers and students would not need to wear masks indoors.

However, the Department of Public Health later tweeted that it would be providing clarification “regarding masking enforcement, recognizing local schools’ experience in keeping students and educators safe while ensuring schools fully reopen for in-person instruction.”

Under the new guidance, students will be required to wear a mask indoors, along with adults while sharing indoor spaces with students.

Schools must also provide a face covering to those who inadvertently fail to bring one to school. Those who refuse will not be allowed on campus.

“In order to comply with this guidance, schools must exclude students from campus if they are not exempt from wearing a face covering under CDPH guidelines and refuse to wear one provided by the school,” officials said.

CDPH said schools should offer “alternative educational opportunities” to students who refuse to mask.

Some exemptions apply, including those who have “a medical condition, mental health condition, or disability that prevents wearing a mask” along with the hearing impaired.

Masking outdoors will be optional.

CDPH said that the agency would continue to assess the mask requirement and will decide whether to update them by November 1.