“I’m really, really happy that we’ve had the flexibility to go below six feet,” said Ben Lummis, superintendent of Gloucester Public Schools, which has traced just three coronavirus cases to in-school transmission this year. “It’s meant that many, many more kids have the chance to be in school, where we think they should be.”
That has quickly made the Centers for Disease Control and Prevention’s emphasis on six feet one of the most controversial elements in the school reopening debate, sparking complaints and confusion among school leaders and criticism from experts who say scientific evidence does not support the need for greater distance if other mitigation measures are in place.
“Six-foot, strict social distancing in most districts means you can’t bring everyone back into the building, and you will be in some sort of remote learning … it’s ginning up to becoming one of the major flash points,” said Benjamin P. Linas, a Boston University associate professor of epidemiology and infectious-diseases doctor who last month joined 300 experts to urge Massachusetts’s education commissioner to stick with three feet.
In a letter, they said in-school transmission in the state had been “exceedingly rare,” even amid high community spread, and that the “risks to students of not being in school are dramatic.”
That argument was bolstered Wednesday by a new study, published in Clinical Infectious Diseases, that found similar coronavirus case rates of students and staff in 48 Massachusetts districts that adopted a three-foot distancing minimum and 194 that opted for six. The authors’ conclusion: Schools with mask mandates can reduce distancing “without negatively impacting student or staff safety.”
The latest CDC guidance advises schools in communities with low or moderate coronavirus transmission to implement six feet of distancing “to the greatest extent possible.” But it refers to that distance as “required” in places with substantial or high transmission, which under the agency’s rubric included the vast majority of the country. Those should operate under hybrid or remote models, it said.
The CDC says studies show in-person schooling is not a major driver of community spread and that in-school transmission is typically lower than or similar to community levels when combined with mitigation protocols including hand-washing, mask-wearing, ventilation — and physical distancing.
“I can’t point to any specific number [of feet] that’s going to tell you that this is zero risk,” said Linsey Marr, an expert in airborne virus transmission at Virginia Tech, who said she supports a less-than-six-foot distance in schools implementing other safety measures. “It comes down to your own risk tolerance and risk benefits. I have kids in school, and I can see how important it is for them to be in school in person.”
‘Six feet isn’t this bright dividing line’
The six-foot distancing guideline that has been dogma in the United States for a year is rooted in research that began in the 19th century on how far droplets emitted by sneezes and coughs flew before falling. Many scientists say it is outdated. They now know those larger droplets are well-blocked by masks — but also that the coronavirus spreads via smaller aerosol droplets that can linger in the air, travel much farther and leak to varying degrees from the sides of many masks.
Six feet “at this point is not really relevant for aerosols, which behave like cigarette smoke,” Marr said. “The farther the better, but six feet isn’t this bright dividing line.”
With that in mind, scientists from the Massachusetts Institute of Technology and the University of Oxford proposed a graded approach to risk based not on distance, but on an activity’s setting, length and occupancy level, as well as its ventilation and whether participants are masked. In their rubric, a full class of masked children — sitting indoors for hours — might be medium- or high-risk, depending on ventilation.
“Three feet is not recommended, unless it has been carefully assessed for a particular room, activity, and high-grade masking is in place at all times,” Bourouiba said. “The risk of exposure to the fresh and dense breathing zone of others is too high at three feet. In addition to distancing to avoid direct breathing zone exposure, air venting and patterns have to be optimized.”
But other experts say masking and ventilation improvements appear to lower that risk enough to justify reopening schools even where community spread is substantial — particularly for young children, who are less vulnerable to severe covid-19 and appear to transmit the virus less efficiently than adolescents and teens.
Marr and other experts point to a systematic review, published last summer in the Lancet, of 172 studies on the coronaviruses that cause covid-19, SARS and MERS. It found that distancing of at least one meter, about three feet, was associated with a “much lower risk of infection.” The WHO’s one-meter recommendation for schools is based on that review, spokesman Tarik Jasarevic said in an email.
Unpublished research from the Mayo Clinic, based on simulations showing how well masks blocked aerosol particles emitted from mannequins, also found that physical distancing dramatically reduced exposure between an unmasked target and unmasked source. But when both wore masks, the risk was negligible at one, three and six feet.
Ventilation upgrades can also lower risk, and they don’t have to be expensive, said Richard L. Corsi, an indoor air quality expert at Portland State University. A portable HEPA air filter can significantly reduce the “inhalation dose” of aerosol particles, he said.
“A $20 box fan that you buy at Target can bring a lot of air in” when fitted in an open window, Corsi said.
Advocates of reduced distancing also point to a recent CDC study on in-person schooling in a rural Wisconsin county where community spread was high. From late August to the end of November, the incidence of covid-19 in 17 schools was lower than in the community, and just seven of 191 staff or student cases were traced to in-school transmission.
In those schools, lead author Amy Falk said in an interview, few ventilation improvements were made, and distancing was “all over the board.” Half of elementary students were seated between three and six feet apart, and one-third sat less than three feet apart. In secondary schools, she said, most students were six feet apart in class, but not in hallways.
“My son’s in first grade, and they’re very close — they’re doing math projects on the floor together,” said Falk, a pediatrician. “They’re masked, but they’re really playing together.”
But other scientists urge caution. The value of six feet lies not just in separating people, but in lowering density, said Donald Milton, an aerosol expert at the University of Maryland.
“What makes a difference is the number of people in a room,” Milton said. “If there are fewer people in the room, it’s less likely there’s a source of infection in the room. That’s why I think it works.”
‘Folks are really pleased. Their kids are in schools.’
In Massachusetts, where about 20 percent of students are learning remotely and many others are in hybrid models, state officials are forging ahead with a plan to compel schools to fully reopen this spring. The state chose a three-foot distancing minimum last summer based on WHO recommendations and the experiences of schools in Europe and Asia, and it intends to keep that, said Jeffrey Riley, the state’s elementary and secondary education commissioner.
“Now we see that vaccines are rolling out, our numbers are going down, and brighter days are ahead, and we need to begin the process,” of eliminating remote and hybrid learning, Riley said in an interview.
In a statement, the Massachusetts Teachers Association cited the CDC guidance and said Riley and Gov. Charlie Baker (R) “chose to ignore the science.”
Distance is also being debated in the town of Brookline, outside Boston, where the school district is proposing to reduce its parameter from six to three feet. An eight-page “evidence of scientific consensus” — produced with the help of a parent panel packed with Linas and other experts from the area’s many scientific institutions — summarizes its argument: Mitigation has worked in the district, and the cost to children is mounting.
“I’m not saying that it’s safe to pack kids into buildings under any circumstances in a covid-denialist way,” Linas said. But, he added, “we can’t react to theoretical fears when we have real damage being done to kids and families right now. All the evidence we have suggests we can do it safely if we do it well.”
In Gloucester, where about 80 percent of students receive in-person instruction, the CDC guidance did not make waves, Lummis said. Parents and teachers have gotten used to the three-foot rule, which is used in schools where space limitations demand it, he said. Spreading out and adding teachers has allowed middle-schoolers, for example, to stay six feet apart.
Things are hardly normal. Students attend school only for half-days, because state rules still require six feet of distance when eating — an unmasked activity scientists say may be the riskiest part of a school day. The buildings could not accommodate that, Lummis said.
“We make it day by day, and it’s incredibly challenging,” he said. “But folks are really pleased. Their kids are in schools.”
So pleased, he said, that in-person enrollment is rising. Now Lummis foresees a new distance-related challenge on the horizon: Even at the three-foot minimum, some classrooms may not be big enough to fit everyone who wants to come.
Laura Meckler contributed to this report.