New data shows a recent uptick of COVID-19 virus levels in local wastewater — a trend that, while unsurprising, has caught the attention of some public health experts.

“We've seen this the last several times when school has come back in session,” said Andrew Lover, an assistant professor of epidemiology at UMass Amherst. “But it is a bit concerning that it's so sudden and pretty high and [in] just a short period of time.”

In the past week, tracking by Biobot with the Massachusetts Water Resources Authority has shown a slight upswing in sewage viral numbers — from a seven-day average of 637 and 497 gene copies per mL on September 21 in the agency’s South and North systems, respectively; to a seven-day average of 1104 and 1081 RNA copies per mL, respectively, on September 27. (By comparison, the levels during the post-holiday, omicron-fueled spike at the beginning of January easily topped 6,000 copies per mL for several days in both systems.)

“It's not a dramatic surge, but it is an increase,” explained Dr. Dan Barouch, director of the Center for Virology and Vaccine Research at Beth Israel Deaconness Medical Center. “We certainly want to keep a close eye on it.”

Advocates for increased COVID safety protocols in Boston Public Schools are at least one group that have taken note of the latest wastewater data. The group BPS Families for Covid Safety, or FamCOSa, told GBH News that it has already heard reports of “outbreaks” in schools two weeks into the new school year.

“BPS has yet to define what they consider an ‘outbreak’ and/or state what specific protective measures will be instituted,” FamCOSa’s statement read. “We believe that now is the time for universal masking, weekly PCR testing and greater attention to ventilation and filtration in the Boston Public Schools.”

Case counts, which often lag days or weeks behind wastewater data, largely remained steady Thursday.

Lover said part of the reason for this recent increase has to do with waning booster shots. The state's most recent weekly COVID report, published Wednesday, shows less than half of people in their 20s have gotten at least one booster; just over half for people in their 30s; and 59% for those in their 40s.

“The booster uptake is a bit lower than we had all hoped for,” he said. “And so quite a lot of people are getting to probably the end or near the end of their protection.”

Looking overseas, the trends elsewhere don’t spell out a good future.

“Right now, currently, the United Kingdom is seeing quite a quite a large wave,” Lover said. “And they are a few weeks ahead of us.”