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Coronavirus levels in Boston-area waste water continue to plunge

MWRA's Deer Island treatment plantDavid L. Ryan/Globe Staff

In another encouraging sign that Omicron may be loosening its grip on the state, the amount of coronavirus detected in Eastern Massachusetts waste water has continued its dizzying decline in recent days, according to data released Thursday by the Massachusetts Water Resources Authority.

The numbers have dropped to less than a quarter of their Omicron-fueled peaks early this month, though they remain higher than they were during last winter’s surge.

Officials from Cambridge-based Biobot Analytics, which conducts the testing, say they have found that the amount of virus detected is correlated with newly diagnosed coronavirus cases several days later. So the declines in the amount of virus suggest there may be further declines in cases ahead.


Waste water from 43 communities, including Boston, converges on the MWRA’s Deer Island treatment plant. There, the sewage is tested to determine the number of SARS-CoV-2 RNA copies per milliliter of waste water.

The MWRA reports data for two regions, southern and northern. For the southern region, the seven-day average was 2,634 RNA copies/mL as of Thursday. That’s down from a high of 11,446 RNA copies/mL on Jan. 3.

In the northern region, the seven-day average was 2,061 RNA copies/mL as of Thursday, down from 8,644 as of Jan. 5.

“It’s a very encouraging trend,” said Dr. Paul Sax, clinical director of the Division of Infectious Diseases at Brigham and Women’s Hospital.

But he warned, “There’s still plenty of COVID out there, hence caution still warranted, especially for immunocompromised people.”

Martin Finucane can be reached at martin.finucane@globe.com.