Teachers spread the coronavirus to other staff and students in recent outbreaks in Georgia schools.
Inadequate masking and distancing also may have contributed to in-school transmission.
Combining multiple prevention strategies is the best way to avoid an outbreak.
A new investigation has found that teachers were central to COVID-19 transmission in elementary schools.
The findings suggest that prioritizing school staff in the ongoing vaccine rollout could potentially reduce the spread of the virus in schools, allowing for safer reopenings.
The Centers for Disease Control and Prevention investigation took place in Cobb County, Georgia, where nine COVID-19 outbreaks occurred at six elementary schools between December 1, 2020, and January 22, 2021. The CDC identified 32 student cases and 13 educator cases across the schools, and at least 18 household contacts of those infected also tested positive.
At least two of the infection clusters began with educator-to-educator spread and continued as teachers exposed students to the virus, the report found. Teachers tested positive in all but one of the clusters.
"In all clusters, educators played an important role in the spread of COVID-19 in the schools," CDC public affairs specialist Jasmine Reed told Insider in an email. "Although there was COVID-19 spread from student to educator and from student to student, these happened less frequently."
Teachers shared the virus during lunch and passed it on during class
Although the schools required students and staff to wear masks, some may have spread the coronavirus when they removed their face coverings to eat lunch.
After observing the schools, the investigators determined that transmission between educators likely occurred during in-person meetings or lunches in at least two clusters. The teachers could have then exposed students to the virus in the classroom.
This particular transmission pattern led to half of the student and teacher cases in the two schools in question, the report found.
Inadequate masking and distancing may have also led to infections
If the students had been properly masked and sat at a distance, the spread of the virus within the classroom could have been better contained.
But despite the schools reporting high levels of mask compliance, the CDC investigators learned in interviews that not all students wore their face coverings correctly, and some didn't wear them at all.
Additionally, students in this district typically sat less than three feet apart with plastic dividers between them. Distancing at six feet apart wasn't possible given the high turnout and classroom layout, but experts have told Insider that partitions alone aren't enough to stop the spread of the tiniest virus-laden droplets.
Students also ate lunch in these classrooms, so it's possible that some student-to-student transmission could have taken place during that unmasked period.
Multiple layers of precaution can help prevent outbreaks
Past CDC investigations have found that it is possible to avoid and mitigate COVID-19 outbreaks with simple preventive measures.
Overnight camps in Maine managed to nip potential outbreaks in the bud by screening campers and counselors upon arrival this summer. Although two staff members and one camper tested positive, the camps saw no secondary transmission and enjoyed a near-normal summer.
The camps combined multiple strategies including early identification and isolation, quarantining, masking, physical distancing, and cohorting campers in small groups.
A similarly multi-layered approach was also effective in childcare settings, according to a Pediatrics study published in December.
"It's like a piece of Swiss cheese," Laura Blaisdell, lead author of the Maine report, previously told Insider. "Every layer has a limitation, and it's the putting of the layers on top of each other that allows us to cover up those holes."
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