Mask mandates were effective as the Delta variant of the coronavirus was driving a surge in Covid-19 cases across Missouri, according to an analysis that the state’s Department of Health and Senior Services conducted in early November.

But the state did not immediately share that data with the public. Instead, the information was released on Wednesday, a month later, because of a public records request by The Missouri Independent, a nonprofit news organization that reported the findings, and the Documenting Covid-19 project at the Brown Institute for Media Innovation.

The records include an email dated Nov. 3 from the director of Missouri’s Health Department to a staff member in the governor’s office. The email included two graphs that compared the rates of reported Covid-19 cases and deaths in parts of Missouri with and without mask mandates.