Thread by @jeffgilchrist

COVID-19: Impact of mask policies and school outbreaks

The CDC has released two studies looking at the impact of mask policies on school associated COVID-19 outbreaks. Policy makers in Ontario please note, "school-associated outbreaks" so they *do* actually happen. 🧵1/

The first study looked at grades K-12 in Arizona from July to August 2021 when schools resumed in-person learning. The CDC found that schools without mask requirements were 3.5x more likely to have COVID-19 outbreaks ( cdc.gov/mmwr/volumes/7… ). 2/

Mask requirements were variable by school and only 21% of schools had mask requirements from the start of schools reopening, 30.9% enacted a mask requirement a median of 15 days after school started, and 48% had no mask requirement. 3/

They found 191 school-associated COVID-19 outbreaks with 8.4% in schools with early mask requirements, 32.5% in schools with late mask requirements, and 59.2% in schools without a mask requirement. 4/

The second study looked at 520 U.S. counties from across the country where the CDC found that counties (62%) without school mask requirements experienced larger increases in pediatric COVID-19 case rates ( cdc.gov/mmwr/volumes/7… ). 5/

Looking at the graph, the first thing you can notice is that the # of COVID-19 cases per 100k population of children was much lower before the start of the school year than just after school starts. This makes it pretty obvious that transmission is happening in schools. 6/

You can also see the dark blue bar graph entries for counties without school mask requirements are much higher than their mask requirement counterparts. This study similarly found a 3.5x higher difference in cases for counties without masks in schools. 7/

The bottom line is that masks are making a significant difference in reducing the amount of transmission and outbreaks at schools. 8/

Universal masking in schools is reducing the amount of outbreaks and transmission happening in school which then in turn reduces the amount of transmission back into the community. 9/