In this Jan. 3, 2022, file photo, people wait in line for COVID-19 testing at West End House in Boston. Credit: Suzanne Kreiter / The Boston Globe via AP

BOSTON — The closely monitored Boston-area COVID-19 wastewater data have started falling in the past few days, sending an encouraging signal to local infectious disease experts who are “cautiously optimistic” about this virus drop.

After local wastewater samples spiked more than 100 percent over the previous two weeks — along with an increase in reported virus cases during the omicron BA.2 variant wave — the most recent update from the wastewater tracker shows the sewage data has taken a downward turn.

The north-of-Boston COVID wastewater average has fallen 13 percent in the past few days, and the south-of-Boston average has gone down 8 percent. The sewage data are the earliest sign of future virus cases in the community.

“I think that we may be starting to turn the corner on this most recent small wave of infections,” said Davidson Hamer, a Boston University School of Public Health infectious diseases specialist. “I have been speculating that the current secondary BA.2 wave would be shorter and less intense than the preceding omicron wave.

“This would fit in with my hypothesis that so many people were infected with omicron that there are relatively small parts of the Massachusetts population that have not already met and become infected with this variant,” he added.

As the wastewater climbed over the past several weeks, the daily average for cases in the Bay State jumped from about 600 infections in mid-March to nearly 2,000 cases last week.

That increase in reported infections is much lower than the omicron peak in January.

“I can’t think of a time when we’ve seen the wastewater data go down before we saw a really strong uptick in cases, so it’s unusual,” said Matthew Fox, a Boston University School of Public Health epidemiology professor.

“But that wastewater data has been such a reliable predictor of what is going to happen that I’m cautiously optimistic that this may mean that what we had hoped, that this wave will be a much smaller wave, will be true,” he added.

Both of the epidemiologists noted that the past week has been school vacation week, and that many people have been away.

“Since many families are away for the school vacation, it is also plausible that their absence could have resulted in a reduction in fecal shedding of viral RNA in the greater Boston area,” Hamer said. “It will be interesting to see if this is a further increase next week when everyone is back.

“My hope will be for a continued gradual decline,” he added. “Case numbers have been high but hopefully these too will begin to decline.”

Citing a 65 percent increase in reported COVID cases over the past two weeks, the Boston Public Health Commission on Thursday urged residents to get tested, stay home if not feeling well, keep up to date on their vaccinations, and renewed its recommendation that masks be worn indoors.

Story by Rick Sobey, Boston Herald.