Gov. Steve Sisolak issued an emergency directive Wednesday outlining face mask policies for schools amid a coronavirus surge fueled by the Delta variant.

The directive makes it mandatory for school staff, regardless of vaccination status, to wear face masks inside schools in all Nevada counties. Face masks are also mandatory for all students while on school buses.

But only kindergarten through 12th-grade students in Washoe and Clark counties will be required to wear face masks inside schools. School districts, charter schools and private schools in Nevada’s 15 other counties — all of which have populations under 100,000 — can craft their own indoor face mask policies for students, so long as they don’t conflict with state directives or local health decisions.

The Centers for Disease Control and Prevention last week recommended that school employees, students and visitors wear face masks inside schools, regardless of their vaccination status, to help curb the spread of the virus.

The Clark and Washoe county school districts already followed suit with that advice and have required face masks for students and staff. Students in those school districts return on Monday for the 2021-2022 academic year.

Any school that experiences a COVID outbreak must immediately implement a universal face mask policy and enforce it until local health authorities deem it safe to discontinue.

The directive also requires weekly COVID testing for students, staff and volunteered who are not fully vaccinated and will be traveling for sports or other activities.