A team of CDC researchers studied 9 clusters of COVID-19 infections at 6 schools.
In all, 13 educators and 32 students contracted the virus over a six-week period from early December of 2020 to mid-January of 2021.
In two of the nine clusters, which accounted for half of the total number of infections, researchers found the virus was initially spread from one educator to another before being passed on to students.
CDC Director Dr. Rochelle Walensky called the findings, published in the CDC's Morbidity and Mortality Weekly Report (MMWR), "concerning."
"Across the 9 clusters, educators played an important role in the spread of COVID-19 in the schools," Dr. Walensky says. "COVID-19 spread often occurred during in-person meetings or lunches and then was subsequently spread in classrooms."
Dr. Walensky says there were instances where students infected their teachers or spread the virus to other students, but those occurred less frequently.
The two main reasons why the virus spread in the schools, she says, were inadequate physical distancing and inconsistent mask adherence.
The school district had mandated students wear masks in the classroom, except when they were eating.
The schools had also put up plastic partitions between students but did not have enough space to meet the CDC's recommended social distancing guidelines.
"In the schools, physical distancing of at least 6 feet was not possible because of the high number of students in class, as well as because of the classroom layouts," Dr. Walensky says. "In addition, COVID 19 may have spread between educators and students during small group discussions, where educators were in close proximity to students."
Although mask usage was reportedly high, there were breaches, which may also have spread the virus.
"In addition, students ate lunch in their classrooms, which may have also contributed to spread," Walensky said.
The CDC is recommending universal mask-wearing, physical distancing of at least 6 feet, and using cohorting, or "podding," of students to minimize the spread of the coronavirus during in-person learning.
The safety guidelines are especially important, Dr. Walensky says, for schools that have a high rate of virus circulating within their community.
About half of US schools are in counties considered to be in the "red zone," with very high rates of virus transmission.
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