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Every Massachusetts county but one now has a high risk of COVID-19 transmission, according to the Centers for Disease Control and Prevention.
On Sunday, the CDC posted updated transmission data showing that Franklin County is the only one with substantial transmission. The other 13 counties — Barnstable, Berkshire, Bristol, Dukes, Essex, Hampden, Hampshire, Middlesex, Nantucket, Norfolk, Plymouth, Suffolk, and Worcester. — have a high rate of transmission. For weeks, the CDC has been classifying transmission in counties and states as low, moderate, substantial, or high.
This isn’t novel: almost every bordering county in each neighboring state has high transmission.
As of Aug. 29, Massachusetts had a high transmission rate overall, with a 7-day percent positivity of 3% to 4.9% and 146 cases per 100,000 in the last week. Right now, every single state is classified as having a high transmission rate.

These rates have increased slightly. On Aug. 15, only eight of Massachusetts’s fourteen counties had high transmission rates, while the rest were classified as substantial.
Per CDC guidelines posted in July, people in counties with substantial or high transmission rates should be masking indoors, regardless of vaccination status. Municipalities across the state have begun implementing indoor mask mandates, including Somerville, Cambridge, and Boston, but Gov. Charlie Baker has said he’s opposed to a statewide mandate.
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