Experts are seeing hopeful signs in the Boston area’s COVID-19 wastewater data

The wastewater data suggests the region is "over the peak" of omicron infections, though not hospitalizations.

Lane Turner/Globe Staff
Wastewater coming into the Deer Island treatment plant is regularly tested for the presence of the coronavirus. Lane Turner / The Boston Globe

After reaching unprecedented heights just last week, COVID-19 samples from the Boston area’s wastewater are trending sharply downward, suggesting the region is past the peak of the omicron wave.

The average number of coronavirus RNA copies per milliliter collected from both the northern and southern Boston suburbs has dropped by over 40 percent in recent days, according to data submitted Monday to the Massachusetts Water Resources Authority, though it remains higher than the levels found during previous COVID-19 surges.

Dr. Mariana Matus, the CEO and cofounder of Biobot, the Cambridge-based company that analyzes the data, said Wednesday that the change is “meaningful.”

“The MWRA levels have been trending down over the past few days, suggesting that we’re over the peak of Omicron infections,” Matus said in an email.


That doesn’t mean we’re out of the woods yet — especially for short-staffed hospitals, which have bore the brunt of increased hospitalizations due to omicron. While the highly transmissible variant has been generally more mild than previous strains, the sheer, unprecedented volume of infections has still resulted in an increase in patients with serious illness, largely among unvaccinated residents and individuals with underlying conditions.

And according to Matus, there’s been an approximately three-week lag between infections and hospitalization.

“We expect the peak for hospitalizations is still to come,” Matus said.

Experts have said the wastewater data is a good indicator of actual COVID-19 infection rates, since it is unaffected by test capacity and official reporting. Even as Massachusetts averages nearly three times the number of infections as last winter’s peak, wastewater data has suggested the true counts are much higher, capturing unnoticed asymptomatic cases and unreported take-home tests.

While the data this week suggests infection rates remain high, public health experts are welcoming the new downturn.

Dr. Ashish Jha, the dean of Brown University’s School of Public Health, said Wednesday that, nationally, “the peak of this wave is coming into view.”

“Yes, parts of US still rising. And hospitals have many tough weeks ahead. But nationally, wave will crest. And soon,” Jha tweeted Wednesday.

Dr. Bill Hanage, a epidemiology professor at Harvard’s T.H. Chan School of Public Health, also tweeted Tuesday that the drop was “obviously good,” though he warned about increasing infections in older age groups, who “are more likely to require hospital care.” Hanage urged people to get their booster shot to prevent against serious outcomes with the health care system already strained.


“But this suggests good news for the disruption caused by the sheer numbers of infections,” he wrote.

During a live-streamed Instagram conversation Wednesday afternoon with Boston Mayor Michelle Wu, Dr. Sabrina Assoumou, a professor at Boston University’s School of Medicine, noted that the trajectory partly depends on the actions of individuals.

“We get to determine our future,” Assoumou said.

“It seems to be leveling off and getting in the right direction, but to make sure that we stay on that path, we all have to play our role and and right now, given how high the cases are, one of the most important tools that everyone can [use] is to wear a high quality mask in indoor public settings and get vaccinated.”


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