Anyone closely watching the wastewater data noticed a change last week: an uptick in the Northeast's COVID-19 prevalence for the first time since late December 2021. It was up 24% over the prior week. Then, new data as of Wednesday showed the region's numbers falling again, slightly.

It's a mixed signal at yet another uncertain moment in the pandemic. Cases are low, but the CDC estimates the more infectious BA.2 subvariant of omicron is now dominant in the Northeast. Many experts attributed the wastewater increase to BA.2.

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And — for the first time in two years — Tufts Medical Center in Boston has no COVID patients in its ICU.

“Today is the first day since the beginning of the pandemic, specifically March 23, 2020, when we admitted our first COVID ICU patient, that we started the day with zero COVID ICU patients,” hospital epidemiologist Shira Doron said Thursday.

Doron said the recent spike in wastewater levels bears watching, but experts are not overly concerned.

“We are always going to be cautiously optimistic,” Doron said. “We are always going to be reluctant to declare the pandemic over and the worst behind us, I think forever more.”

Dr. Matthew Fox, a professor in the departments of epidemiology and global health at Boston University, says the rise in Boston’s wastewater follows a similar pattern to an rise in cases in Europe with BA.2.

“We are seeing the Boston wastewater case numbers, or the Boston wastewater projections are starting to go back up, which suggests that that's probably driven in part by this new variant,” Fox said.

“I don't think that's cause for panic at the moment because, you know, we are in a much more mature stage of the epidemic than we have been previously,” Fox said, adding that “we’re starting to get to the point where future waves are not nearly as severe as prior waves.”

Even after detecting the uptick, Cambridge-based Biobot Analytics noted in a Twitter thread that the rise in wastewater still leaves the virus concentration at 3% of levels at the omicron surge’s peak.

The Massachusetts Department of Public Health uses wastewater surveillance as an early indicator of COVID-19’s prevalence in a community, usually preceding trends in case counts by several days or weeks.

Fox says the amount of virus transmission at this stage of the pandemic depends on three variables: interactions between people, steps to reduce the spread such as masking and community immunity, which is reliant on vaccines and prior infection.

Though Massachusetts has a highly vaccinated population, residents are starting to gather with one another more frequently — and Fox warns that, with a more infectious variant circulating, cases will start to go back up.

But many people who are immunocompromised or who live with chronic illnesses and disorders are afraid to let down their guard. 25-year-old Britt Dorton, who lives in Chicago and has Ehlers-Danlos Syndrome, uses her Twitter account to ask people to think of disabled people and continue to wear a mask.

“It’s such a small act,” she told GBH News, “and I don’t know what to say to anyone whose response is that they don’t care about our lives.”

Dorton works from home and rarely goes out. She said it’s important to continue to be mindful of others who are at greater risk, even if people are tired of quarantining or limiting socializing.

“It really is a matter of life or death for us,” she said.

Even with less severe variants, COVID-19 carries risks of death or long-term health impairments. Doron pointed out that the vast majority of COVID-19 cases in the United States now are omicron, which is more contagious.

“It ebbs and flows, and increases and decreases are really what we can expect for the future for an indefinite period of time, whether it's weeks, months, years or decades,” Doron said. “It’s hard to say.”