In this Nov. 30, 2020, file photo, a city employee talks on his phone wile taking a break from laying down the basketball court floor in the Portland Expo. Credit: Troy R. Bennett / BDN

Mainers should now wear masks when they are in Kennebec, Somerset and Waldo counties because of rising COVID-19 transmission rates.

Kennebec County became on Saturday the newest addition to the list of counties where even vaccinated people have been recommended to wear masks. That county currently has 50.1 cases per 100,000, up from 49.28 the day before.

Those recommendations were already in place in Somerset and Waldo counties, where active cases stood at 55.42 and 111.28 per 100,000 people, data show.

In Hancock County, those recommendations have been dropped because cases have slipped to 49.45 per 100,000, down from 53.11 the day before.

The U.S. Centers for Disease Control and Prevention recommends people wear masks indoors regardless of vaccination status if there is substantial transmission of the virus in their community, defined as 50 or more cases per 100,000 people at a county level.

A few months ago, all Maine counties were above that level. Now most of them are below it, but the relatively small populations of some counties can lead to quick swings in the data.