Out of 3,500 students, just 234 coronavirus infections were documented during the fall semester, the researchers reported in a pre-print study posted online.
Just 9% of students who brought new infections to school infected others, the researchers found.
“There was no evidence of student-to-teacher or teacher-to-student transmission in either school,” they wrote.
“To our knowledge, this is the only, comprehensive and long-term study that tested all K-12 students (asymptomatic) and staff from August through December – making it the only one where we really see disease incidence in this age group and true spread in schools,” Dr. Darria Long of the University of Tennessee Department of Emergency Medicine, who worked on the study, told CNN.
The team studied two independent K-12 schools, not named. One was described as being in the Southeast and one in the Mid-Atlantic. Each school followed the US Centers for Disease Control and Prevention’s guidelines for preventing spread of the virus, including social distancing and mask use. They also implemented “aggressive” laboratory screening testing policies.
School officials performed contact tracing with every positive case.
“The infected person and those within close proximity or where a potential breach of protective measures could be determined were tested, quarantined, and asked to quarantine and report any symptoms,” the researchers wrote.
“As community rates rose in the fall, the schools tested specific populations such as athletes more frequently. They also tested the entire school population after the Thanksgiving break. Officials also encouraged parents to report any test results obtained outside the school.
At one school, 4.9% of students, faculty and staff tested positive and at the other, just 2% did.
“Seventy two percent of in-school transmission cases in School A were associated with noncompliance with school mask wearing rules. Of known off-campus sources, the major ones identified were family exposure, including siblings returning from college; off-campus activities, including parties and other gatherings,” they wrote.
“The largest outbreak at School A was linked to a non-school sanctioned, sports-related event.”
However, the source of most cases was never determined.
“Children do contract Covid-19 and can transmit it, but rates of illness when they are in school are lower than rates of illness when they are out of school, suggesting that children and communities may be at lower risk when children are in school,” Long said.
“This could be because mitigation measures in the controlled school environment (that are not possible when children are not in school) can significantly suppress transmission.”
In the first study, researchers looked at data on 17 K-12 schools in rural Wood County, Wisconsin, that conducted in-person learning last fall. They found lower Covid-19 case rates than in the community at large, and few cases of in-school transmission.
Contact tracing and investigation determined that seven of those 191 cases — 3.7%, all among students — were contracted in school.