LANSING, Mich. (AP) — Berrien County in southwestern Michigan on Sept. 1 ordered masking inside all schools, pointing to a rapid increase in COVID-19 transmission over the past month.

Once Washtenaw County follows suit, nine of 83 counties — including many with the largest populations — will require face coverings in schools. The office of Gov. Gretchen Whitmer, who has refrained from reinstating a statewide mandate that was in place last academic year, said mask policies do or will cover at least 57% of kids in traditional public schools.

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Berrien’s order applies to all educational settings, including colleges and child care centers. In their order, acting health officer Courtney Davis and medical director Rex Cabaltica cited a four-fold increase in coronavirus cases in August compared with July and noted only 35% of 12- to 19-year-olds are vaccinated.

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“Our top priority is keeping students in school for in-person learning,” Davis said in a statement, adding that “masking is one of the best defenses against COVID-19 transmission.”

A spokeswoman for the Washtenaw County Health Department confirmed it will issue a mask order Thursday. Nine of 10 K-12 districts already have some type of requirements, but policies are more mixed among private schools, Susan Ringler Cerniglia said.

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