Real-World Study Supports the Value of Masking in Schools to Prevent COVID-19

By Reuters Staff

December 09, 2021

NEW YORK (Reuters Health) - As the Delta variant of COVID-19 took hold, schools in North Carolina that implemented universal masking maintained low within-school transmission rates, a new study shows.

Dr. Daniel K. Benjamin, Jr, of Duke Clinical Research Institute in Durham, North Carolina, and colleagues examined within-school transmission during emergence of the Delta variant in 20 North Carolina school districts.

The analysis included 783 K-12 schools in 19 counties, with 59,561 students and 11,854 staff who attended in-person instruction between June 14 and August 13, 2021. The percentage of fully vaccinated residents in the 19 counties ranged from 32% to 65%, with an average of 47% of eligible residents vaccinated as of August 1.

All districts implemented universal masking of students and staff during the study period, regardless of vaccination status. No schools had to shut down due to COVID-19 cases during the study period, the authors report in Pediatrics.

"This report demonstrates that even with exponentially rising community cases at the start of the Delta variant surge, schools that implemented universal masking retained low within-school transmission," Dr. Benjamin and colleagues write.

The findings are "notable," they say, because the Delta variant of SARS-CoV-2 is much more infectious than ancestral strains.

In the community, on average, one person infected with the Delta variant subsequently infects eight others. However, in schools implementing universal masking, it would take 13 attendees who acquired COVID-19 outside of school to infect one person inside schools, the authors estimate.

"Although extremely encouraging that secondary transmission in schools with universal masking remains lower in schools than in the community, the 2.6% secondary attack rate observed in the setting of the Delta variant is slightly higher than the rate of roughly 1% observed when ancestral and Alpha strains were predominant in North Carolina, likely reflecting the more infectious nature of Delta," the authors add.

These data, coupled with previous reports of widespread school-based infection from a single unmasked index case in places like California, "reinforce the importance of vaccine uptake among those eligible, strict adherence to masking, and avoidance of pandemic fatigue," they write.

They note that while this study did not compare masked to unmasked settings, recent studies from schools without an early mask mandate in July and August 2021 had 3.5 times the odds of school- associated COVID-19 outbreaks compared with schools that had mask requirements.

The authors of a linked editorial say state actions to restrict masking requirements within schools present a "critical public health challenge, and inadequate masking in schools has likely contributed to the increased burden of COVID-19 among children <18 years of age."

"This surge of infections has overwhelmed pediatric emergency rooms and hospitals across the country as new hospital admissions nearly doubled for pediatric patients 0 to 17 years between January and September 2021 (0.29 to 0.50 admissions per 100,000 population), based on CDC data," write Dr. Tony Yang with George Washington University in Washington, D.C., and colleagues.

"In addition to the health care burden, rising pediatric cases are taxing school systems that are struggling to adapt infection prevention and control measures to the rapidly changing COVID-19 landscape. Several school districts without masking mandates have had to either close or modify instruction because of rising COVID-19 cases," they point out.

"These statewide bans on school mask mandates directly contradict evidence-based public health recommendations," they add. "State masking bans notwithstanding, strong evidence supports masking as an effective COVID-19 mitigation strategy, particularly among those, such as school-aged children, who are not yet eligible to receive a COVID-19 vaccine."

They say "local school districts should be able to take actions, including mandating masks, to protect students and to keep schools open for in-person learning."

SOURCE: and Pediatrics, online December 8, 2021.