The Maine CDC’s guidance about indoor mask use now applies to half of the state.

The agency said last month that it was recommending indoor mask use for everyone in areas of high or substantial transmission of the coronavirus. Those distinctions are made by the U.S. Centers for Disease Control and Prevention.

Eight of Maine’s 16 counties were listed by the U.S. CDC as having high or substantial transmission on Thursday. Waldo County was listed as having high transmission, and Penobscot, Piscataquis, Somerset, Cumberland, York, Lincoln and Kennebec counties were listed as having substantial.

York and Cumberland counties account for nearly 40% of the state’s population.

The rest of the counties in the state were listed as having low or moderate transmission.