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The controversy over how much physical distance is necessary to safely reopen schools may be inching to a close.

During a press call with reporters, infectious diseases physicians flagged new evidence suggesting that whether kids are separated by 3 feet or 6 feet in schools doesn't affect COVID-19 case counts substantially.

The study, conducted in Massachusetts and published in the journal , found that it "really did not make a difference" to keep kids 6 feet apart versus half that, said Tina Q. Tan, MD, of Northwestern University's Feinberg School of Medicine and Lurie Children's Hospital of Chicago, on the press call, which was hosted by the Infectious Diseases Society of America on Thursday.

Moreover, data over the last year have shown that the schools themselves do not appear to be "super-spreading" environments, Tan said.

Any outbreaks that may have happened in schools were tied to exposures in the community or occurred in schools without any protective protocols in place, she said.

Three Feet vs Six

The nonrandomized study compared COVID-19 rates in 242 Massachusetts school districts, some of which kept students 6 feet while others maintained 3-foot separations over a 16-week period from September 2020 to January 2021. Student case rates were similar in districts with ≥3 feet versus ≥6 feet of distance between students (rate ratio 0.891, 95% CI 0.594-1.335) after adjusting for rates of SARS CoV-2 in the community.

Among school staff, districts with ≥3 feet versus ≥6 feet of physical distancing also showed similar case rates (RR 1.015, 95% CI 0.754-1.365).

Based on these findings, study authors led by Westyn Branch-Elliman, MD, MMSc, of Harvard Medical School and the VA Boston medical center, concluded that "[l]ower physical distancing policies can be adopted in school settings with masking mandates without negatively impacting student or staff safety."

Tan noted that the CDC now recommends that "the 3-foot distance can be used in those situations where the teachers are fully vaccinated with two doses of COVID-19 vaccine." She stressed that physical distancing is still very much a part of the recommendations for schools, along with universal masking, hand hygiene, cohorting of students and teachers, and using outdoor space "whenever possible."

Kids Needed for Herd Immunity

Participants on the call also addressed a thorny problem that hasn't gotten much attention yet: how to achieve herd immunity to COVID when children are excluded from vaccination.

Tan said at least 70% of the population needs to be immune, either through vaccination or natural infection, to reach herd immunity -- meaning there are no longer enough potential hosts for the virus to continue to circulate.

In the U.S., 25% of the population is people younger than 18. Given the number of adults refusing vaccination, that would make herd immunity unattainable through vaccination unless children and teens are included.

Tan noted that pediatric availability is coming but will likely happen in phases.

Pfizer has finished enrolling a clinical trial for older children (age 12 and up) and Moderna currently has a trial underway in adolescents.

Findings from these trials are expected "by either the end of the spring or in early summer," Tan said, which means that vaccination for these adolescents and teenagers could start before schools end their summer break.

Asked whether K-12 schools might require students to be vaccinated, Tan said that's still not known, but is "a possibility."

As for the timeline for herd immunity, Tan said, "there's still going to be some people that are vaccine hesitant or anti-vaccine and ... that's in both the adult population as well as in the pediatric population."

There's always a possibility that new variants could circulate for which the vaccines are less effective, she noted, and if that were to happen, then Americans would need either a vaccine booster or a different vaccine, she said.

"Right now nobody knows when you're going to reach herd immunity," Tan said.

Even if the U.S. reaches that 70% threshold, that wouldn't prevent people in other parts of the world from bringing the disease in, she noted.

"It's just one of these questions that, you know, you think about, and then it gets bigger and bigger and bigger."

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