With COVID-19 cases climbing and the return to classes less than a month away, Gov. Gretchen Whitmer issued guidance Wednesday urging — but not mandating — Michigan schools require masks for students and staff.

The new guidance follows U.S. Centers for Disease Control and Prevention recommendations that everyone in public schools mask up in classrooms and buses regardless of vaccination status. The guidance also urges schools to maintain at least three feet of distance between students.

You can read the recommendations here.

“We are committed to ensuring Michigan students and educators are safe in the classroom, including those who may not yet be vaccinated,” Dr. Joneigh Khaldun, chief medical executive and chief deputy for health at the Michigan Department of Health and Human Services, said in a statement Wednesday.

While state officials called it “crucial” for schools to follow CDC guidelines about masks, the lack of a mandate means policies will differ from district to district.

“We have district leaders who go to school for years to be education experts, but they are not trained to be medical experts,” said Peter Spadafore, deputy executive director of the Michigan Association of Superintendents and Administrators. “They need support from state and local medical experts to make these decisions.”

Lou Steigerwald, superintendent of Norway-Vulcan Area Schools in the Upper Peninsula, said the new guidance only adds to the stress felt by school leaders over what to do this fall.

”It is extremely frustrating to see these recommendations issued with ever stronger language, but falling short of mandates,” Steigerwald said. “I strongly suspect that the folks issuing these recommendations know how controversial masks are in many areas. Issuing ‘recommendations’ instead of mandates is only making things more heated for schools.

“It does let the recommendation issuers off the hook though,” Steigerwald said, “which is why I believe they issue them as they do.”

Determining just how safe Michigan’s classrooms are from the virus is complicated.

Educators were among the first in line to be eligible for vaccination, and as a group, are more highly immunized than the state as a whole. In April, a survey of 22,000 members of the Michigan Education Association, the state’s largest teacher union, found that 86 percent were partially or fully vaccinated.

But the children inside those teachers’ classrooms are less protected.

Children under the age of 12 are not yet eligible for COVID-19 vaccinations, and as of Friday, just 41 percent of youths 16 to 19 years old, and 31 percent among those 12 to 15 years old, are vaccinated, according to state data.

In all, about 58 percent of Michiganders age 12 and older have had at least one dose of vaccine.

Meanwhile, the state’s case rates, positivity, and hospitalizations continue to rise.

Although nowhere near the levels seen in the fall and spring surges, recent data shows a slow but steady gain by the virus in recent weeks, likely driven by the highly transmissible Delta variant. The variant had been detected in sampling of COVID vases in at last three dozen counties scattered throughout the state, as of Tuesday.

Outbreaks doubled in a single week, according to a data review released Wednesday. Those factors undoubtedly pushed virus transmission to “substantial” or “high” levels in 31 of Michigan’s 83 counties, according to mapping by the Centers for Disease Control and Prevention.

Still, transmission remained low in at least seven counties, and hospitalizations remained low as well, especially among children. Just 9 of the 513 patients hospitalized for suspected or confirmed COVID were pediatric patients.

In all, Michigan’s average daily case count of about 700 is a tenth of what it was in April.

Facing surges in many parts of the country, the CDC in July recommended universal masking for all staff, students and visitors in K-12 schools, regardless of vaccination status. The American Academy of Pediatrics made a similar recommendation that everyone in a school setting over the age of 2 wear face masks.

Whitmer said Monday she hoped schools would follow the recommendations of the CDC and Michigan Department of Health and Human Services and mask up.

“We know that the Delta variant is spreading, that it remains a very serious concern and that children cannot be vaccinated yet under 12, and that’s why we really are strongly encouraging districts to adopt masking policies,” Whitmer said.

“It’s an unfortunate part of the moment that we’re in, but this variant is a real concern.”

State Superintendent Michael Rice echoed Whitmer’s concern in a statement Wednesday. “Our students and staff need to be in schools as much as possible this year,” Rice said. “Following the informed guidance from national and state health experts will help keep our students and staff healthy and help maximize student learning.”

The Michigan Department of Health and Human Services has the authority to issue mandates in health emergencies, but for now it hasn’t.

MASA’s Spadafore said school leaders would prefer that medical experts give them a firm yes or no about face masks. Short of that, Wednesday’s guidance does give “one data point that district leaders will use in making those decisions,” he said.

That leaves decision-making to officials in the state’s 891 traditional school districts and charter schools. Ann Arbor Public Schools and Kalamazoo Public Schools have announced plans for students and staff to wear masks at least for the beginning of the school year.

In Gibraltar School District in Wayne County, Superintendent Amy Conway said the district will follow any mandates that are issued. Until then, “we will have masking optional, but that could change at any time depending on conditions and on what the Wayne County Health Department recommends,” Conway said.

Several school officials said mask mandates in classrooms will be hard to enforce unless the mandates apply to other indoor gathering locations, like movie theaters, offices and restaurants.

Some businesses have taken it upon themselves to impose mask requirements. Automakers last Tuesday announced they were reinstating mask mandates in their plants.