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MDHHS data: Preliminary correlation showing higher case rates in counties where school districts are not masking

A KN95 mask and a surgical mask.
Photo illustration by Max Posner/NPR
A KN95 mask and a surgical mask.

A weekly update from the Michigan Department of Health and Human Services finds that “cases in children are increasing and case rates are higher in counties where school districts (are) without masking.”

The state looked at the correlation between school districts’ mask rules and county level cases in the week ending on September 10.

The blue dot here represents a school district. It was then paired with the new case rates among school-age kids in the county where the district is located. (And if the district is in more than one county, where most of the school district is located in.)

COVID-19 case rates in the week ending Sept. 10. (The data is of Sept. 13.)
Michigan Department of Health and Human Services
COVID-19 case rates in the week ending Sept. 10. (The data is as of Sept. 13.)

In this analysis, the state found that the case rate range is higher in counties where school districts do not have mask rules. And that COVID-19 cases in children are increasing in counties where school districts do not have mask rules.

One of the researchers is Marisa Eisenberg, an epidemiologist at the University of Michigan. She said they also looked at mask rules and cases both at the county level and saw the same pattern.

But Eisenberg also explained the analysis does not prove the lack of a mask mandate is leading to the higher case rates. In other words, correlation does not prove causation.

"It might be the counties that didn't have mask rules, also didn't have a lot of other things,” she said. “Maybe there's more social contact happening in those counties in general. But it is the case that there's a correlation there."

And it is, at least with preliminary numbers, a “pretty strong” correlation.

It is important to use every strategy to protect kids, especially those who are not eligible to be vaccinated yet, she said.

"We want to put as many mitigation strategies in place as we can so that students can be in person in school as much as possible while minimizing the amount of transmission and new cases that we see," Eisenberg said.

Currently more than 40% of Michigan school districts require masks.

The Michigan Parents Alliance for Safe Schools is petitioning the state to issue a statewide mask mandate for schools.

The MDHHS analysis also found that over the school reopening period (Aug. 18 to Sept. 8, also known as the earliest to latest first day of school), the largest percent increase in the 7-day average of new COVID cases was among young people under 18. In fact, 12-to-18-year-olds jumped up by 96%. It was up by 57% percent for kids 11 and under.

“Even if you expect some amount of transmission, because there's more people coming together back to school and all of that. It doesn't, it's still not good, right?” Eisenberg said. “It’s still something that we want to minimize and it's important for kids to be able to go back to school, but we want to make that as safe as we possibly can. And so, I do think that the increases in transmission that we've been seeing are a number of outbreaks of the increases in cases among the 0-to-18 age groups. Those are worrying trends.”

Case rates are increasing for all age groups in the 7-day rolling average, with trends highest for 10 to 19-year-olds.

COVID is considered to be milder for younger age groups, but young people could potentially experience even more severe outcomes. The delta variant is much more contagious than previous variants.

Eisenberg said the development and social needs of children are important.

“But also, of course, you need to keep them safe, and make sure that they're not getting sick and not getting COVID and not potentially transmitting it to the rest of the family,” she explained.

MDHHS’s weekly data update shows that K-12 schools saw 71 new outbreaks as of Sept. 13 — the setting with the greatest number of outbreaks. (School outbreaks are considered easier to identify.) There were also nine new outbreaks associated with childcare settings.

Nisa Khan joins Michigan Radio as the station’s first full-time data reporter. In that capacity, she will be reporting on data-driven news stories as well as working with other news staff to acquire and analyze data in support of their journalism.
Kate Wells is a Peabody Award-winning journalist currently covering public health. She was a 2023 Pulitzer Prize finalist for her abortion coverage.
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