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By Catharine Richert and Elizabeth Shockman, Minnesota Public Radio News

State officials are warning of a growing number of COVID-19 cases in schools across the state.

As more districts open up for in-person instruction, state health officials say 752 Minnesota schools have confirmed COVID-19 cases as of this week.

Based on genomic sequencing of confirmed cases, state officials estimate that 50 percent of the COVID-19 cases in Minnesota right now are the so-called B.1.1.7 variant — a more contagious and, additional research suggests, a more severe version of the virus.

In a statement, state epidemiologist Dr. Ruth Lynfield said the Minnesota Department of Health is growing concerned by the increase in cases among school-aged children and teens.

Simultaneously, they’re seeing more hospitalizations.

“That’s why it is so important for all of us to keep doing those things that make a big difference: wear masks, keep social distancing, avoid large gatherings, adhere to other restrictions that are still in place, get tested, stay home if you’re ill or test positive, and roll up your sleeve and get vaccinated as soon as you can,” Lynfield said.

Over the weekend, University of Minnesota public health expert Michael Osterholm said on “Meet the Press” that what Minnesota is seeing with circulation of the B.1.1.7 variant stands to shift the push to reopen schools.

“Right here in Minnesota we’re now seeing the other aspect of this B.1.1.7 variant that hasn’t been talked much about,” he said. “It infects kids very readily. Unlike the previous strains of the virus, we didn’t see children under eighth grade get infected often or they were not frequently very ill. They didn’t transmit to the rest of the community. That was why I was one of those people very strongly supporting in-person learning. B.1.1.7 turns that on its head.”

The number of Minnesota schools reporting COVID-19 cases has risen steadily since early January. But state Health Department data does not distinguish between variants when reporting cases.

More than 90 percent of Minnesota schools now offer some form of in-person learning to their students. That number is expected to rise when the Minneapolis and St. Paul districts welcome more students back to classes in mid-April.