As Anusha Viswanathan warned of a rise in coronavirus cases in Bucks County and called on the Central Bucks School District to protect still-unvaccinated children, a sign bobbed next to her: “No Mandatory Masks.”

Opponents and supporters of mask mandates hovered around Viswanathan, a parent and pediatric infectious-disease physician, as she and others favoring masking in schools addressed a crowd of parents and reporters gathered outside before a school board meeting Tuesday night. One woman used her sign reading “Trust Doctors, Follow Science, Protect Our Students” to try blocking an anti-mask message from TV cameras.

“Murderers!” someone shouted, visibly rattling Viswanathan. At another point, a woman holding a “Masks Save Lives” sign shoved the sign at another woman, striking her over the head.

The intense scene, captured by TV and cellphone videos circulated on social media, played out hours after the federal Centers for Disease Control and Prevention called for everyone in K-12 schools to be masked this fall — ramping up its recommendations as the delta variant fuels a rise in cases nationally, and while children under 12 remain ineligible for vaccination.

After hours of comments from 70 members of the public, the Central Bucks School Board voted to stick with its mask-optional plan.

Whether to require masks in schools is a major debate in Philadelphia-area districts. Some said this week they still aren’t planning to require masks, at least for now. The Philadelphia School District says it will require everyone to wear them, regardless of vaccination status, while the Upper Darby School District will require masks for children 11 and younger. Montgomery County on Thursday said it’s recommending universal masking in schools, but the decision is up to individual districts.

» READ MORE: Internal CDC document shows COVID-19 delta infections are more severe than earlier variants, and vaccinated people may spread it

Area school leaders say that vaccination rates in their communities are higher — and COVID infection rates lower — than in other parts of the country, and that they didn’t see the CDC’s guidance as one-size-fits-all.

“The CDC’s always going to recommend things. And then we have to look at the risk tolerance in our community,” said Upper Dublin Superintendent Steve Yanni, whose district is “strongly encouraging” masks for unvaccinated students but not requiring them.

Still, he says he doesn’t know what will happen before the school year begins — and is reminding parents that the plan could shift.

“The next two weeks will really be pivotal,” Yanni said in an interview Wednesday, before Montgomery County had revised its guidance to align with the CDC’s school-masking recommendations.

The CDC updated its guidance this week as cases surge in communities where vaccination rates are lower, and amid evidence that the more contagious delta variant is causing breakthrough infections — which are generally mild — among vaccinated people.

But it isn’t a requirement. While Pennsylvania has said it recommends schools follow the CDC guidance, Gov. Tom Wolf’s administration said this week it isn’t considering reinstating a statewide mandate.

“These are really local decisions. And I think each community is in a different place in terms of making these decisions,” said David Rubin, director of the Children’s Hospital of Philadelphia PolicyLab. The calculus for schools is different this year, Rubin said, because adults — who are at greater risk for severe illness than children — have been eligible for vaccination.

» READ MORE: CDC advises masking indoors where cases surge and in all schools, as delta variant spreads

What could push schools to adopt stricter measures would be more significant infections in vaccinated people, and more prevalent severe illness in children, Rubin said. In reviewing national data, “we have not seen any disproportionate rise” in children who become severely ill from COVID compared with adults, Rubin said.

In recommending everyone wear masks indoors, Philadelphia health officials recently said they were concerned about a small increase in hospitalizations of children too young to be vaccinated.

The Montgomery County Health Department on Thursday endorsed universal masking in schools, regardless of transmission rates. Earlier in the week, the department had advised schools to look at the rates in their districts in making masking recommendations.

“What we’re doing is we are making as much information as we can available to our school districts so that those elected school boards can work with their superintendents to make the decision about their specific communities,” County Commissioner Val Arkoosh said in an interview earlier Thursday.

Other area counties have not issued similar guidance, and it isn’t clear at what point they might do so, or how some schools would decide to adopt more preventative measures.

At a school board meeting last week, Haverford Township School District Superintendent Maureen Reusche said that if the district — which has been planning a mask-optional start — moved into “a high rate” of transmission of the virus, “we feel that it is the responsible thing for us to look at masks for unvaccinated staff and students.”

But “I do not have the rubric for how we’re going to check that at this point in time,” said Reusche. She noted that of 156 comments the district had received about its health and safety plan, “every comment was about masking.” A spokesperson said this week the district “will continue to monitor positivity and incidence rates.”

West Chester Area School District Superintendent Jim Scanlon said his district would be working with the county Health Department, which he expects to put out “some direction” in the near future. (A county spokesperson did not respond to questions this week about upcoming guidance.)

“Here’s the good news: We’re talking about a mask,” Scanlon said. “It was so much more complicated a year ago.”

» READ MORE: What the new CDC and Philadelphia mask guidelines mean for the Philly region

Masking doesn’t have to be an all-or-nothing choice, Rubin said. If cases rise, schools could consider requiring masks in crowded hallways, for instance, but not classrooms. He also noted masking could become increasingly important if the virus begins to spread, to keep students in school and avoid quarantines.

Some parents are raising concerns about school plans that go beyond masking policies. Mariam Mahmud, a Central Bucks pediatrician and school board candidate, was among the group objecting to the district’s fall plan, which “has nothing in it. No mitigation, no layered strategy,” she said, adding that some parents and medical professionals are “really feeling worried and concerned.”

The district says it will aim for three feet of social distancing when possible, but its plan approved Tuesday says it will not notify close contacts or issue communications for COVID cases.

The district’s acting superintendent, Abram Lucabaugh, said that if a family informed their school of a child’s COVID case, the school could respond. But it would be “untenable” for the district to contact-trace, he said, because the county Health Department is no longer doing so.

County spokesperson Larry King said in an email that the Health Department is not currently planning to contact-trace this fall, because it is “no longer an effective tool for us.” Schools “are free to do whatever notifications they think are necessary” regarding positive cases, he said.

At the Central Bucks School Board meeting, masks were the biggest topic. One mother said her second grader struggled, as masks made it hard for her to understand what her teacher or friends were saying.

Then two classmates got COVID, and “what saved her” was the shift to virtual learning, so that “she could see their faces. She could see they weren’t dying,” the mother said, pleading: “Please do not make them go backwards. Because we have no idea what this is doing to their mental capacities.”

» READ MORE: School board meetings turn tense with debates over critical race theory and masking

Another mother, however, likened masks to other public safety measures. She had her 8-year-old son vaccinated against HPV, not for his sake, she said, but at the advice of his doctor and for the future safety of others.

“We do a million of these things. We do them all the time,” she said, urging the board to “make the unpopular choice. Go with the safer option.”

Other parents argued that masks were a personal choice, and vowed to ramp up the pressure if the district moved to require them.

“There are no government mandates to hide behind anymore,” Lisa Sciscio, a school board candidate, told the board. “It’s just you.”

Staff writer Erin McCarthy contributed to this article.