As the Omicron surge begins to recede in many regions of the country, the governors of New Jersey, Connecticut and Delaware have announced that they will lift school mask mandates in the coming weeks.

But the move to loosen these politically charged restrictions has divided scientists and public health experts. Some cheered the change.

“I think it’s entirely appropriate that we start lifting school mask mandates now,” said Joseph Allen, a Harvard University researcher who studies indoor environmental quality, including in schools. “We’re in a much better place than we were before, and it’s time to update our strategies to reflect the moment.”

Others noted that the virus was still exacting a significant toll on the country, with cases about as high as during last winter’s peak and more than 2,500 Americans dying each day. Lifting school mask mandates too early could jeopardize the progress that the country has made over the last few weeks, some health experts said.

“We’re just starting to get it back under control,” said Seema Lakdawala, a respiratory virus researcher at the University of Pittsburgh, noting that many young children remain unvaccinated. “I don’t think we should be abandoning the interventions we have that are still helpful.”

Experts agreed that mask mandates should not last forever and that officials needed to clearly explain what criteria would be used in deciding when to lift them. But there is still debate over what those metrics should be and whether certain places in the country had met them.

“I think we’re moving to a place where it will make complete sense to remove mask mandates,” said Justin Lessler, an epidemiologist at the University of North Carolina at Chapel Hill. “Maybe we’ll be there in two to three weeks. Personally, I would like to see people wait until cases are low rather than anticipating that they will be low at some future date.”

School mask mandates have been among the most contentious public health measures implemented in response to the pandemic. Opponents of mask mandates have often pointed to the lack of randomized, controlled trials on the effects of masking in schools and have highlighted flaws with specific studies that have documented benefits of masking.

They have noted, for instance, that schools that require universal masking may differ in many ways from those that don’t, and that in a world brimming with confounding factors, it is difficult to conclusively prove that mask-wearing reduces viral transmission in schools.

But a growing body of evidence — from laboratory experiments to real world studies conducted around the world — suggests that masking provides benefits in a variety of settings, including schools, scientists agreed.

“You can pick apart any one study,” said Linsey Marr, an aerosol scientist at Virginia Tech. But, she noted, “there’s overwhelming evidence that masking has a beneficial and small effect on reducing transmission in schools.” (Although the effect is small on average, individual students and teachers can gain more personal protection by wearing high-quality, well-fitting masks, she noted.)

Even the experts who believe that it is time to lift school mask mandates said that such policies have been an important strategy at certain phases of the pandemic. But, they note, the country is no longer in the same position it was in 2020 during the first waves of the pandemic in the United States.

Vaccines are now widely available for all adults and for children 5 or older. And although Omicron can evade some of the body’s immune defenses, making breakthrough cases more likely, the vaccines continue to provide protection against hospitalization and death.

In communities where vaccination rates are high and the Omicron wave is receding, it makes sense for officials to begin thinking about lifting mask mandates, including in schools, some scientists said.

“Once you don’t have a lot of virus, and you have a highly vaccinated community, you move from masking required to masking optional,” said Dr. Carlos del Rio, an infectious disease specialist at Emory University.

Dr. del Rio recommended that communities also pay close attention to local hospitalization rates and capacity when making decisions about masking policies. If local hospitalization rates are below 10 new Covid admissions per 100,000 residents per day and I.C.U.s are less than 80 percent full, it makes sense to remove mask mandates, he said.

Dr. Allen, the Harvard researcher, noted that hospitalization rates, which were already low for children, have fallen in the Northeast, with 0.4 admissions per 100,000, according to data from the Centers for Disease Control and Prevention. That is lower than the hospitalization rate for vaccinated adults, who are now typically able to dine out mask-free.

“But for kids with the same risk, even unvaccinated kids with the same risk, we’re keeping more strict policies in place,” he said.

Keeping mask mandates in place beyond when they are necessary risks undermining the public’s trust in health officials, Dr. Allen said. In the event of future surges, officials may need to renew school mask mandates, but they should lift them when conditions are better, he said.

“Kids can tolerate this, and when it’s necessary to do so, it’s fine for them to mask,” Dr. Allen said. “But we shouldn’t do it for one second longer than necessary.”

Ideally, local officials should be prepared to lift and reimpose school mask mandates as conditions change, experts said.

Zoe McLaren, a health policy expert at the School of Public Policy at the University of Maryland, Baltimore County, recommended that school officials do regular surveillance testing to monitor whether the virus is prevalent within the school population — and be prepared to adjust their mask policies accordingly.

“If schools are well-ventilated and there’s low transmission in the schools, then they’ll have few cases,” she said. “Then lifting a mask mandate in that school would make more sense.”

But officials tend to be reluctant to make these kinds of frequent shifts, she noted.

States that lift school mask mandates now may find it difficult to reimpose them in the future, said Julia Raifman, a health policy expert at Boston University who leads the Covid-19 U.S. State Policy database.

Dozens of states had mask policies in 2020, she said; now, few of them do. “So that shows you how hard it is for anywhere to turn back on mask policies after they’ve turned them off,” she said.

And while the absolute risk to children may be small, child hospitalization rates have increased during the Omicron surge, she noted.

Moreover, school mask mandates are not simply about protecting children, some scientists said.

“People will say, I am sure, that it is a mild disease in kids, so why are we concerned?” Dr. Lakdawala said. “The concern is that it can then continue to spread in our communities.”

Children who catch the virus at school could also pass it on to more vulnerable adults, said Mercedes Carnethon, an epidemiologist at the Northwestern University Feinberg School of Medicine. Winter was the wrong time to ease up on masking in schools, she added.

“To take away masks now during the winter months, when most interactions are indoors, is a mistake that will lead to school outbreaks,” she wrote in an email.

She added that while it “would be ideal” if the mask mandates remained in place until children under 5 were eligible for vaccination, that may not be feasible, given how long the authorization of vaccines for young children was taking.

“I am cognizant that there is an urgency to identifying an off-ramp,” she said.

The lifting of school mask mandates means that many parents will have to make these risk-benefit calculations on their own, deciding whether to have their children continue wearing masks in the classroom.

“The things that you’d want to think about is, is your kid vaccinated?” Dr. Marr said. “Does your kid have underlying health conditions that might put them at higher risk? Is your kid in an especially crowded classroom that has poor ventilation? All of those factors would increase the risk.”

Studies suggest that masks, especially high-quality, well-fitted ones, can protect the wearer.

“If you’re looking for a good mask, focus on filtration and fit, the two Fs,” Dr. Allen said.

Although N95 masks are not designed for children, there are other respirators, such as KF94s, that come in children’s sizes. But even a well-fitting surgical mask or multilayered cloth mask can help provide protection, scientists said.

“Masks are most effective when everybody wears them,” Dr. Lessler said. “But they are still effective individually when only you wear them.”