Covid-19 outbreaks are far more likely in schools that don't require students and staff to wear masks, new data from the US Centers for Disease Control and Prevention shows.
Two studies released Friday support the agency's recommendation for universal indoor masking in schools.
One study in Arizona showed schools with no masking requirement were about 3.5 times more likely to have a Covid-19 outbreak than schools that had a universal masking requirement.
A second study showed counties across the US where schools required mask use also had less transmission of the virus in the community in general.
For the first study, researcher looked at data covering about 1,000 K-12 schools in Arizona's Maricopa and Pima Counties, which are home to more than three-quarters of the state's population.
A school was considered to have a masking requirement if all people -- including students, staff, faculty and visitors -- were required to wear a mask indoors, regardless of vaccination status. A school was considered to have an outbreak if there were two or more news cases among students or staff within a 14-day period, beginning a week after school started.
From mid-July through the end of August, 191 school-associated outbreaks occurred, according to the CDC. Schools with universal masking requirements in place at the start of school accounted for about 31% of the set of schools analyzed, but only about 8% of outbreaks. Meanwhile, schools with no masking requirement accounted for 59% of those outbreaks, but less than half (48%) of the total set of schools analyzed.
In early August, the CDC adjusted recommendations for masking in schools to include everyone, regardless of vaccination status, due to the prevalence of the more contagious Delta variant.
"I would say that data actually absolutely show that masking decreases outbreaks in schools," CDC Director Dr. Rochelle Walensky said Monday. "So with the purpose of keeping our kids in school, getting them in school, having them be safe, masks really are the way to go."
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