With the school year underway virtually in many Philadelphia-area districts, some health experts are saying the time may be right to bring some children back to classrooms.

After advising schools last month to delay reopening, in part to account for possible spread of the coronavirus after Labor Day gatherings, David Rubin, a pediatrician who directs the Children’s Hospital of Philadelphia PolicyLab, said this week that “we haven’t seen a huge resurgence” in the wake of the holiday weekend, and after college reopenings.

“We might see a second window opening up here in mid- to late September” for schools to bring back students, said Rubin, who, along with CHOP colleagues and a University of Pennsylvania physician, has been providing guidance to superintendents in the Philadelphia region, including in Delaware, Chester, and Montgomery Counties and a few in Bucks County.

In Montgomery County, Val Arkoosh, a physician and county commissioner, agrees that schools have a window to reopen toward the end of the month. She noted the county had opened camps and child-care facilities over the summer with “minimal to no transmission.”

“With our current burden of disease here in the county, we had a successful summer, so I do think it’s possible,” she said.

Whether schools can safely reopen is case-specific, Rubin and Arkoosh said, depending on local case counts and whether schools can facilitate social distancing. Achieving six feet of spacing between students, as recommended by CHOP and Pennsylvania officials, has been a challenge for many schools.

While some school districts around Philadelphia have opened with in-person instruction, many started the year online — some citing CHOP’s advice to wait until Labor Day effects had been observed.

Now some are planning to bring students back. The Lower Merion School District intends to open Sept. 29 for kindergartners, adding grade levels for hybrid in-person and virtual sessions in successive weeks. The Central Bucks School District — which had cited staffing shortages rather than transmission rates for its virtual start — will return all students Sept. 30, some for full in-person instruction and others under a hybrid model.

The Garnet Valley School District is starting in-person instruction Monday for some special education students, followed by kindergartners through second graders on Sept. 29 and then older grade levels.

“We were really starting in virtual to give us some time to see if we would see a spike in the infection rates,” Superintendent Marc Bertrando said. “As of today, at least in Delaware County, we haven’t seen that resurgence we were worried about.”

In Chester County, there has been a recent increase in cases. Salwa Suleiman, a pediatric infectious disease physician at Nemours Children’s Health in Wilmington, told the Unionville-Chadds Ford school board Monday that the county’s jump in incidence rates from about 30 to 40 cases per 100,000 residents in August to 71.3 cases by Sept. 4 was “very concerning.”

Suleiman, who said the rise may have stemmed from a “super-spreader” event involving a cheerleading team in a Downingtown-based school, noted Chester County Health Department guidelines call for incidence rates to be stable for three consecutive weeks before schools transition to a more in-person model.

If the county’s cases “continue to increase or stay at this high rate over the next two weeks,” Suleiman told the board, “virtual instruction will have to stay.”

In an interview, Suleiman said that “in general I would agree" with CHOP’s recommendation that schools could consider reopening. But it’s too soon to know whether the bump in Chester County will mean continued spread of the virus, she said.

Rubin said Chester County’s numbers “came down a bit this week” and were declining along with those in Montgomery, Delaware and Bucks Counties. He also said the numbers likely reflected college screenings, and noted that outbreaks so far at schools like Temple University haven’t seemed to spread widely through the community.

Rubin and others are monitoring the incidence rate of the virus in the community to gauge the risk of transmission in schools. Montgomery County has been maintaining a rate around 30 cases per 100,000 people, per week, county officials said.

At that rate, Rubin said, and assuming positive test results represent only a portion of the true number of infections, a school of about 1,000 might have three cases. With social distancing, mask requirements and a cleaning regimen, that might be a small enough number to prevent the coronavirus from spreading through the school.

“What we’re trying to do now is, if we can get to a period where people are really adapting to these protocols, we’ll try to get as many kids back as possible by mid-October,” Rubin said.

PolicyLab in August specified thresholds for community transmission that could warrant reopening schools. With “stable or declining weekly case incidence between 10-35 per 100,000 AND less than 5% test positivity,” the group advised schools to consider an “incremental reopening strategy,” returning younger and special-needs students to classrooms first.

Rubin said this week that Philadelphia, with an incidence rate of 50 per 100,000, might be safe to have some schools reopen.

The thresholds CHOP recommends “are not absolutes, but need to be interpreted alongside the size of enrollment, and the strength and confidence" in school safety plans, Rubin said. He also said data continue to suggest elementary school children may be less susceptible to symptomatic infection, and less likely to transmit the virus.

Arkoosh, in Montgomery County, said she believed studies evaluating whether young children were more or less likely to transmit COVID-19 had not yet reached clear conclusions. But she thought younger children should be prioritized for returning to classrooms due to their struggles with virtual learning.

She expects schools would be safe to operate on at least a hybrid model unless the rate of tests that came back positive, currently about 3% in the county, neared 7% or 8%.

Pennsylvania has issued guidelines on when schools can consider reopening, but has not mandated specific action. Some districts began the year planning to remain virtual for months — among them the Cheltenham School District, which plans to return in January.

Given how transmission rates change, Superintendent Wagner Marseille said, the district wanted to provide consistency with a virtual model.

“Because this is so fluid, 30 days ago what they were saying is very different than what they are saying right now," Marseille said.

While the district is monitoring the virus' spread, it isn’t immediately reevaluating its reopening plans, Marseille said, adding that improvements in the data aren’t the only consideration.

“It’s one thing what the data says. It’s another thing in terms of people’s individual levels of comfort,” he said.

Rubin warned it was likely the virus will surge in the winter, and could lead to schools shifting to all virtual learning for periods of time.

Bertrando, of Garnet Valley, said reopening will be a challenge: With some students learning in school buildings and others at home to ensure social distancing, teachers will have to juggle instructing both groups at once. And the district may face difficult decisions if the virus spreads and it has to consider closing again.

“Just getting the kids in is probably the easiest hurdle. Keeping kids in” is the challenging part, he said.