The CDC compared COVID-19 case numbers between schools in Alabama that had mask rules and schools that did not.

Researchers found that school districts that required a mask from students and staff had a lower COVID-19 rate of 23%.

School districts that only had partial mask requirements, like requiring masks in classrooms but not the gym, also had a lower incidence rate than schools without mask requirements. But still not as low as schools with full mask mandates.

Some schools went from having no mask policy to having a partial or full mask policy.

In those schools, researchers observed that COVID-19 cases were better in comparison to COVID-19 cases in their communities.

The CDC said the study shows that “wearing a mask in K-12 schools is an effective way to help prevent the spread as COVID-19 levels rise in a community, especially in communities with high COVID-19 levels”, which could open the doors to a change in mask guidance as the pandemic evolves.