BOSTON (WHDH) - Four counties in Massachusetts are now considered high risk for COVID-19 transmission, while eight others are at a substantial risk, according to the Centers for Disease Control and Prevention.

RELATED: Nantucket issues indoor mask mandate amid ‘significant increase’ in COVID-19 cases

The latest data from the CDC shows that Bristol, Barnstable, Dukes, and Nantucket counties have a high COVID transmission rate, with more than 100 new cases reported per 100,000 residents between July 28 and Aug. 3.

Berkshire, Hampden, Worcester, Middlesex, Essex, Suffolk, Norfolk, and Plymouth counties all have substantial transmission rates, with between 50 and 99.99 new cases reported per 100,000 residents in that same seven-day period.

Franklin and Hampshire counties are said to have moderate transmission rates, meaning there have been between 10 and 49.99 new cases reported per 100,000 residents in the last seven days.

The CDC now recommends that vaccinated people return to wearing masks indoors in every Massachusetts county that is at high or substantial risk because the COVID-19 Delta variant is fueling a surge in new cases.

Bay State health officials on Thursday reported 1,046 new COVID-19 cases, two additional deaths, and a seven-day positivity rate of 2.61 percent.

Since the start of the pandemic, there have been 677,433 confirmed cases in Massachusetts and 17,725 deaths.

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