Only 5 school-associated COVID-19 cases were detected among students and teachers exposed and tested across 20 schools in the district.
The rare school-associated infections were attributed to poor mask usage or close lunch seating.
Schools can reopen safely even when seating is 3 feet apart if other measures like masks are heeded, the CDC says.
Rates of COVID-19 transmission were high in Salt Lake County, Utah, this past December and January, but in one school district, they remained very low thanks to mitigation measures like mask-wearing, a March 19 report out of the Centers for Disease Control and Prevention found.
Specifically, only 0.7% of teachers and students who'd been in close contact with an infected peer or colleague contracted COVID-19 from them at school. None of the 20 schools analyzed experienced a coronavirus outbreak.
The authors say the report demonstrates how mitigation measures like mask wearing and restricting extra-curricular activities can make school reopenings safe - even, as was the case in the schools studied, kids can't always sit a full six feet apart.
In accordance with this report and other studies, the CDC changed its physical distancing guidance for K-12 schools Friday, saying 3 feet of space is enough between students, in most circumstances.
The school-associated cases were traced to improper mask wearing or close seating at lunch
To conduct the study, CDC researchers looked at 20 K-6 schools in one Salt Lake County school district between December 3, 2020 and January 31, 2021.
They identified 1,041 students and teachers susceptible to COVID-19 who, while at school, were in close contact with 51 of their COVID-positive peers and colleagues. "Close contact" meant they'd been with the infected person, while contagious, for 15 minutes or more in a classroom, cafeteria, school bus, or at recess.
After testing 735 of the 1,041 contacts, the study authors found only 12 had contracted the disease, and only five had contracted it at school. In those school-associated cases, transmission seemed to occur because the infected person wasn't wearing their mask properly or was sitting near someone at lunch.
Wearing masks and staggering breaks can prevent transmission even if some students and teachers are COVID-positive
The study authors credit the school's mitigation strategies with preventing higher rates of spread and outbreaks in schools.
For example, students were put in cohorts where possible, and most schools staggered lunch, gym, and other activities like library use and art classes. They also limited, or made virtual, in-person extra-curriculars and events like sports, assemblies, performances, and field trips. 86% of teachers reported that their students always wore their masks, except when eating and drinking.
Such strategies proved successful, despite the fact that kids were spaced a median of 3 feet apart, and teachers often had closer than 6-feet interactions with their kids in small group settings without any plexiglass or other barrier.
Even when the school district loosened its quarantining guidance in mid-December - only requiring a close contact of an infected person to quarantine if one or both hadn't been wearing masks - rates of school-associated COVID-19 cases didn't change. That guidance shift led to over 1,200 student in-person learning days saved, the report says.
This could be a model for other schools
The study had some limitations. For one, the genome-sequencing technology to differentiate school-based transmission from community transmission wasn't always available. Plus, some contacts of infectious people could have been missed, and some identified contacts may have already been unknowingly immune to COVID-19. The findings also can't be applied to new COVID-19 variants that weren't circulating in the Utah community at the time.
But the study authors say the Utah schools can serve as a model for others looking to resume in-person learning safely.
"When ≥6 ft distancing is not feasible," they write, "schools in high-incidence communities can still limit in-school transmission by consistently using masks and implementing other important mitigation strategies."
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