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‘Incredibly encouraging’: Coronavirus level in Eastern Mass. waste water is down 98 percent from peak

Sewage arriving at the Deer Island treatment plant on Boston Harbor is tested for traces of coronavirus.David L. Ryan/Globe Staff

Good news. The level of coronavirus detected in sewage in Eastern Massachusetts has continued to plummet, suggesting the Omicron-fueled surge is still dwindling, according to the latest data from the Massachusetts Water Resources Authority.

The level of coronavirus detected from communities in both the MWRA’s southern and northern regions has now dropped by 98 percent from when it peaked early this year.

Levels haven’t fallen this low since late July of last year when numbers were rising again after bottoming out in late spring and the first few weeks of summer.

“I find the latest data incredibly encouraging,” Joseph Allen, an associate professor at Harvard’s T.H. Chan School of Public Health and director of the Chan School’s Healthy Buildings Program, said Wednesday.


He said experts had worried that the decline of the virus might stall, but so far that hasn’t happened.

“When Omicron hits, it’s fast and furious, but the declines are steep just like the rise,” he said. “There’s no hint of a plateau just yet.”

The numbers could drop to last summer’s lows, he said.

Waste water from 43 communities, including Boston, the state’s largest city, converges at MWRA’s Deer Island plant on Boston Harbor for treatment before being piped miles into the ocean. The water is tested for traces of the deadly virus.

Officials from Cambridge-based Biobot Analytics, which conducts the testing, say the amount of virus detected correlates with newly diagnosed coronavirus cases several days later. So the declines in the virus levels suggest cases may continue to fall.

“Waste water sampling is one of the best unbiased leading indicators of where we are in the state,” Allen said.

Cases, hospitalizations, and deaths have all been declining.

William Hanage, an epidemiology professor at the Chan School who is also a scientific adviser to Cambridge-based Biobot Analytics, said in an e-mail that the data were “truly heartening to see and it drives home that as we expected while Omicron was not pretty, it was quick.”


He cautioned that “daily death counts remain high” and warned that Omicron is still a risk for the unvaccinated. He also said “vulnerable individuals like the over-65s should seek boosters.”

The testing determines the number of SARS-CoV-2 RNA copies per milliliter of waste water. For the southern MWRA region, the seven-day average was 186 copies/mL as of Tuesday. That’s down from a high of 11,446 RNA copies/mL on Jan. 3.

In the northern region, the seven-day average was 154 RNA copies/mL as of Tuesday, down from 8,644 as of Jan. 5.

Material from prior Globe stories was used in this report.

Martin Finucane can be reached at