BOSTON (WHDH) - Most Massachusetts counties now have either a high or substantial risk for COVID-19 transmission, according to the Centers for Disease Control and Prevention.

The latest data from the CDC shows that Barnstable and Nantucket counties have a high COVID transmission rate, with more than 100 new cases per 100,000 residents reported between July 24 and July 30.

Essex, Middlesex, Worcester, Hampden, Bristol, and Plymouth counties all have substantial transmission rates, with between 50 and 99.99 new cases reported in that same seven-day period.

With the exception of Franklin County, every other county in the Bay State currently has a moderate transmission rate.

The CDC last week recommended that vaccinated people return to wearing masks indoors in parts of the United States where the COVID-19 Delta variant is fueling a surge in new cases.

The guidance on masks in indoor public places applies in areas with at least 50 new COVID-19 cases per 100,000 people in the last week, according to the CDC. That includes 60 percent of counties across the country, eight of which are in Massachusetts.

The change in mask guidance comes amid concerns about the variant’s ability to spread among vaccinated people.

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