TOPEKA — A growing number of Kansas school districts are imposing mask mandates because of the more contagious COVID-19 Delta variant, just before in-person classes resume for the fall.

As of Tuesday, at least nine districts serving more than 92,000 students had imposed a mask requirement at least for students under age 12, who can’t get vaccinated, and most are requiring masks for everyone indoors. The nine districts serve more than 19% of the state’s 476,000 students.

Kansas has seen daily COVID-19 cases increase steadily over the past six weeks, and confirmed Delta variant cases have doubled or nearly doubled every two weeks, according to state data. Kansas also averaged 28 new hospitalizations per day for the seven days that ended Monday, bringing the total to more than 11,700.

In Johnson County, the state’s most populous county, the De Soto school board voted 4-3 on Monday to require everyone to wear masks inside district facilities. The district has about 7,100 students.

“Things have changed quite a bit,” Superintendent Frank Harwood told the board during its meeting. “This is a fluid situation.”

The Centers for Disease Control and Prevention reported Tuesday that only 45.4% of Kansas’ 2.9 million residents were fully vaccinated.

Democratic Gov. Laura Kelly is recommending that K-12 schools require everyone to wear masks indoors or on buses, regardless of whether they are vaccinated. But her guidance has drawn criticism from Republicans, who control the Legislature and who see mask requirements as unnecessary.

Public schools in Kansas start fall classes in August and some school boards are still considering whether to require masks. Topeka’s board plans to discuss mask rules Thursday, and in Wichita, the state’s largest district, the board expects to consider a mask mandate next Monday.

In the 370-student Chetopa-St. Paul district in southeastern Kansas, Superintendent Craig Bagshaw said he plans to ask local school board members next Monday to require masks in school buildings, on buses and during school activities in line with the CDC’s most recent guidelines. Southeastern Kansas has been hit hard by the Delta variant.

“I don’t ask them how to run a school and what curriculum to buy,” Bagshaw said of the CDC. “So why should I not take their recommendations on how to keep people safe? They’re the health professionals. I’m not.”

Meanwhile, Republican state Attorney General Derek Schmidt has asked the Kansas Supreme Court to keep in place a law enacted earlier this year to limit the power of Kelly and local officials to impose COVID-19 restrictions. He is appealing a Johnson County judge’s ruling that struck down the law and wants the lower-court decision put on hold in the meantime.