The transmission rate of COVID-19 is now considered to be "high" or "substantial" in more than half of the state's 14 counties with residents of and visitors to Barnstable and Nantucket counties considered to be the most at risk, according to the Centers for Disease Control and Prevention.
Nine counties now fall under the CDC's updated guidance recommending that masks be worn by vaccinated individuals in indoor public settings in areas of high or substantial transmission. That total is up from five counties when the new recommendations were issued last week.
While Cape Cod and Nantucket are the only areas of "high" transmission, Middlesex, Essex, Plymouth, Worcester, Bristol, Hampden and Suffolk counties are all in the "substantial" transmission category, according to data collected from July 26 to Aug. 1.
The categorization of counties by the CDC was used in the development of the federal government's latest guidance on mask-wearing.
Martha's Vineyard, or Dukes County, fell under the CDC's new guidance last week, but has since been dropped to "moderate" status. Franklin County is the only region of the state rated "low" for transmission, as the delta variant continues to fuel the spread of COVID-19 around the county.
The CDC reports that nearly 61% of counties in the United States are experiencing "high" transmission and another 19% of counties fall in the range of "substantial" transmission.
Gov. Charlie Baker on Friday updated the state's mask guidance to recommend that anyone vaccinated with an underlying health condition or who lives with an unvaccinated or high-risk adult wear a mask when indoors in public. The governor, however, said he thought it would be too confusing to ask residents to keep track of whether they live, work, shop or socialize in counties where transmission status can change from day to day.